Effective protection of essential fish habitat requires understanding fish spatial ecology - lessons learnt from protected European bass nursery areas

Abstract

Spatial management is a widely used technique to protect sessile species or habitats. Protection of essential fish habitat is increasingly being recognized globally within fisheries management policies, requiring further practical assessments within temperate fisheries. We provide a case study for the efficacy of spatially protecting nursery sites for a highly mobile species—the European bass (Dicentrarchus labrax). Using acoustic telemetry, 146 individual fish were tracked for up to 812 days across three independent protected bass nursery areas in the Southwest UK. Within site boundaries commercial fisheries are seasonally restricted to protect vulnerable life stages. Tagged fish were re-detected >5 million times. Detections at receivers highlighted activity hot spots at or near the seaward entrance to each site. Generalized linear modelling estimated high variation in the seasonal presence/absence of fish. Due to variation in the seasonal timing and spatial boundaries of protected sites, the amount of time fish were protected ranged 1.9%–27.4%. Further work is required to link these findings to population processes e.g. mortality, growth or recruitment. We, however, highlight the vital need to consider movement patterns to ensure boundaries of spatially protected areas are relevant to species they are designed to protect.

Introduction

An increasing number of fisheries management policies are highlighting the requirement to spatially protect ‘Essential Fish Habitat’. This is a general term for habitat(s) which provide critical ecosystem services to fish, i.e. habitats that are necessary for spawning, breeding, feeding, or growth to maturity (NOAA 2018; 2025). This concept is a major component of several high-level fisheries policies, which aim to achieve ecosystem based fisheries management, e.g. the Magnus Stevenson Act in USA (USA regulation, P.L. 109–479), the reformed Common Fisheries Policy in the EU (EU regulation, 1380/2013), and Fisheries Act in the UK (UK regulation, 2020 c. 22). Historically, spatial management for mobile finfish was not widely considered feasible due to perceived need to cover large areas which encompass wide-ranging movement patterns (Kaiser et al. 2005, Game et al. 2009, Breen et al. 2015). Studies have, however, since demonstrated the utility of spatially protecting essential habitat to improve biomass of exploited fishes (Jaworski et al. 2006), and/or via spillover increase productivity within adjacent fisheries (Higgins et al. 2008). Protection of essential habitats could therefore complement traditional effort-based fisheries management as well as provide wider societal benefits via improved protection and resilience of seabed habitats (Breen et al. 2015, Sheehan et al. 2021).

European bass (Dicentrarchus labrax) is a commercially and recreationally important finfish native to the Northeast Atlantic and Mediterranean Sea (Pickett and Pawson 1994). The species is targeted throughout its range, with commercial and recreational fisheries worth an estimated £56 million and £172 million per year, respectively (EUMOFA 2020). In 2010, the International Council for Exploration of the Seas (ICES) reported a dramatic decline in the North Atlantic stock (ICES divisions 4.b–c, 7.a, and 7.d–h) (ICES 2024). As a result, in 2015 a suite of technical conservation measures were introduced by the European Commission, which included: (1) a ban on pelagic trawling for bass during spawning periods to protect spawning aggregations of fish; (2) catch restrictions for recreational and commercial fishers; (3) an increase in the minimum landing size from 36 to 42 cm (size at maturity) (UK GOV 2016). In 2016, the population declined below ‘safe biological limits’, and recovery thought to be jeopardy. In 2019, the population levels increased above this threshold; however, relative to historic levels, the population remains in a highly impoverished state (ICES 2024). The decline in the North Atlantic stock is thought to be the result of several issues, including life history characteristics such as slow growth rates (Pickett and Pawson 1994) in combination with unsustainable fishing pressure and successive poor recruitment years (ICES 2024).

Juveniles are known to exploit shallow coastal bays and estuaries as nursery habitat (Kelley 1988; Freeman et al. 2024, Watson et al. 2024). While occupying nursery areas, juveniles will exploit available habitats e.g. salt marshes and mudflats, for both refuge and nutrition (Freeman et al. 2024). Within the first year, individuals are thought to display relatively sedentary behaviour and remain faithful to the same area within a nursery area (Green et al. 2012). In years 2–3 juveniles move more broadly, and may temporarily move into open coastal areas; however, show high fidelity to the original nursery area they occupied as larvae (Pawson et al. 1987, Stamp et al. 2021). In 1990, 34 sites (largely estuaries) were designated across England and Wales (UK) as protected ‘Bass Nursery Areas’ (MAFF 1990). Within site boundaries targeted commercial fishing for European bass was prohibited, there were also restrictions on recreational fishing activities such as prohibitions of specific baits which were thought to be highly effective e.g. live sand eel (Ammodytes sp.). During winter, immature fish were thought to seek thermal refuge in deeper coastal water (Pickett and Pawson 1994). As a result of the perceived absence of European bass from coastal sites within winter (Pickett and Pawson 1994, Doyle et al. 2017, O'Neill 2017), bass nursery areas were predominantly protected on a seasonal basis from 1st May to 31st October (MAFF 1990). There is, however, a large amount of variability in both the seasonal closure period and the spatial extent of bass nursery areas (Fig. 1). As a result of the limited information known on the spatial-temporal distribution of European bass, the efficacy of these protected sites is therefore largely not fully understood.

Mark-recapture studies conducted before and after the designation of BNAs (1988–1994; Pickett et al. 2004) highlighted a potential 25.5% increase in recapture rates, suggesting an increase in juvenile survival as a result of protecting nursery habitat. These figures are likely to be moderated by inter-annual environmental conditions which also impact juvenile bass survival (Watson et al. 2024). However, the results reported by Pickett et al. (2004) demonstrate that spatially protecting important nursery habitat has the potential to provide beneficial effects on population process and can increase recruitment into commercial fisheries. Recent telemetry studies (Stamp et al. 2021, Goossens et al. 2024) have, however, started to challenge the ‘known’ behaviour and coastal residency of this species. Notably, this includes overwintering behaviour within nearshore areas, and inter-annual variability in winter migration timing (Stamp et al. 2021, Goossens et al. 2024). Therefore, as a result of differing spatial and temporal fisheries restrictions within BNA’s (Fig. 1), the relative protection offered to juvenile fish is likely to vary.

As a result of the economic and social significance of this species, it remains important to protect and maximize recruitment to ensure recovery of a highly depleted population. Here we aim to investigate the spatial ecology of European bass within three protected Bass Nursery Areas, and test how well seasonal and spatial closure matches the presence/absence of fish occupying these sites. Our primary research questions are:

1. When and where are juvenile European bass present within protected Bass Nursery Areas and is this affected by seasonal changes in water temperature?

2. How much time are juvenile European bass within protected Bass Nursery Areas?

Field methods

Protected bass nursery areas

European bass were continuously tracked for two years via acoustic telemetry within the following three protected Bass Nursery Areas in the southwest UK: The Dart estuary, Salcombe Harbour and the Taw/Torridge estuaries (Fig. 2 and Table 1) (MAFF 1990). Within the spatial boundaries of the Dart estuary and Salcombe Harbour, the following restrictions apply from 1st May to 31st December. Within the Taw/Torridge, the same restrictions apply from 1st May to 1st November:

• - Targeted fishing for Bass from any vessel is prohibited,

• - Commercially targeting bass is prohibited

Tagging procedure

From June to August 2018, 146 European bass were captured by rod and line via commercial and recreational anglers (Table S1–supplementary information). Each fish was anaesthetized with an induction dose of 70–100 mg/l MS-222 (Tricaine methanesulfonate). Fish were then positioned dorsally on a V-shaped cradle, where they were ram-ventilated with a maintenance anaesthetic dose of 30–40 mg/l MS-222. A single 69 kHz Innovasea V92X transmitter tag (tag dimensions: 29 × 9 mm, 4.7 g—air weight) was implanted within the peritoneal cavity via a small incision (10–15 mm) made slightly off the mid-ventral line between the pelvic fin and anus. Transmitter tags were programmed to emit a randomized uniquely coded ping once every 80–160 s. The surgical site was closed using dissolvable sutures. Analgesic was topically applied to the surgical site (Lidocaine 1% solution diluted to 1:10 with NaCl saline solution). Fish were then monitored within holding tanks (500 l) for a minimum period of 1 h prior to release as close to the capture site as logistically possible. All tagging procedures were conducted under a UK Home Office license (P81730EA5) by personal license holders with PILC entitlement. Dispensation was also provided by the relevant regulatory and land authorities.

Acoustic telemetry receiver array

An acoustic telemetry receiver network was deployed to detect tagged fish within and adjacent to each Bass Nursery Area. Receiver networks were designed to detect European bass movements within Bass Nursery Areas and the open coastline immediately adjacent to the boundaries of each protected site. A total of 78 Innovasea VR2W/Tx receivers were deployed (Fig. 2 and Table 1). This included 35 Innovasea VR2W/Tx receivers on moorings deployed and maintained by the University of Plymouth, plus a further 43 Innovasea VR2W/Tx receivers within the closing lines/seaward entrance on moorings maintained by the relevant harbour authority. The receiver configurations consisted of a series of detection gates that extended up to the mean tidal limit, which had an average spacing of 0.9 km (±0.09), 0.8 km (±0.4), and 1.8 km (±1.6) for the Dart estuary, Salcombe harbour, and the Taw/Torridge estuaries, respectively. Receivers on coastal moorings (managed by the University of Plymouth) were deployed from 22 August 2018 to 18 January 2019 in the Dart, 19 June 2018 to 26 November 2018 in Salcombe harbour and 19 July 2018 to 12 November 2018 in the Taw/Torridge. As a result of storm damage, receivers and moorings were recovered and not redeployed following this period. All receiver stations within the seaward limit of each site (managed by the harbour authority) were deployed continuously throughout the study.

Range testing

Acoustic telemetry receiver detection efficiency was estimated by deploying a range test tag, with comparable power output to those implanted within the fish, in a linear array of receivers in Salcombe harbour. Receivers were spaced ∼150 m apart (Fig. S1–supplementary information). The number of successful detections at varying distances from the range test tag confirmed 60% ping detection at a range of 175 m. The channel width of each tagging site rarely exceeds 300 m; therefore, by positioning receivers at central locations within each channel detection of tagged fish was assumed to be reliable.

Data analysis

Characterizing fish movement/activity

Fish detections were initially screened to identify mortality of tagged fish by applying a movement-based filter during the first 30 days after release (Martínez-Ramírez et al. 2024). A tagged fish was assumed dead if (1) it was never detected; (2) the distance an individual fish swam did not exceed 1 km within 30 days after release. All fish defined as dead were removed from further analysis. Fish activity within each site in relation to Bass Nursery Area boundaries was characterized. The number of individual fish detected at each receiver was averaged per day and qualitatively described in relation to the sites as a whole and the spatial boundaries of each Bass Nursery Area. To assess fish activity in open coastal areas, immediately adjacent to Bass Nursery Areas, fish detections were split to the period of time when open coastal receivers were deployed (i.e. the full system was deployed), and when just the within-site receivers were deployed.

Due to the perceived absence of European bass within coastal sites during winter, which is reflected in the temporal restrictions imposed with Bass Nursery Areas, daily presence/absence of each tagged fish (presence: 1, absence: 0) was calculated throughout the study. Water temperature was measured every hour throughout the study using HOBO U24-002-C loggers deployed at the seaward entrance of each site. Water temperature was then averaged per day and matched to fish presence/absence time series. A binomial Generalized Linear Model (GLMM) (logit link; ‘lme4’, Bates et al. 2015) was then used to estimate the probability of daily European bass presence/absence as a function of site and water temperature. Model simplification (i.e. removal of fixed effects) was conducted and model suitability scored using Akaike Information Criterion (AIC). Following the rules of parsimony, the model with lowest AIC score was selected. If delta AIC scores from models were ≤ 2, the simplest model and/or that with the fewest fixed effects was selected (Zuur et al. 2013). Statistical assumptions were visually assessed via model diagnostic plots.

Efficacy of bass nursery areas

The spatial and temporal boundaries of bass nursery areas vary dramatically between different sites. For example, within the Taw/Torridge the spatial boundaries for the protected bass nursery area are 3–4 km inland from the mouth of the estuary, whereas in other sites they extend to the seaward limit. Temporal protections also differ between locations, where some sites are protected all year vs others which are protected for 5 months of the year. Here we aimed to quantify the amount of time fish are protected within each bass nursery area within the study. We also aimed to investigate how variable spatial and temporal restrictions between bass nursery areas affected the duration of time fish were protected. Specifically, we assessed the potential increase in time fish would be protected if the following were implemented in each site: (1) full spatial protection—bass nursery area, including the entire site from landward entrance to the mean tidal limit; (2) full temporal protection—extending seasonal protection to the whole year; (3) combination of full spatial and temporal protection (Fig. 3).

To assess the impact of these management measures on the time fish were protected, residency periods were calculated for fish on receivers which would be within ‘protected’ Bass Nursery Areas under each management option/refinement. A residency period began when a fish was detected on any receiver within a protected Bass Nursery Area, and ended when a fish was detected on a receiver outside of a protected bass nursery area or was not detected for a period of 6 h. For each fish, the total duration of time within a protected bass nursery area was calculated, then converted to the proportion of time it was tracked (release date: date of last detection). A binomial GLM (‘Stats’, R Core Team 2024) was then used to model the proportion of time fish were protected as a function of site and management option/refinement (Bass Nursery Area, Full Spatial Protection, Full Temporal Protection, Full Spatial and Temporal Protection–Fig. 3 and Table 2).

Results

A total of 146 fish were tagged as part of the study (Table S1–supplementary information) (Dart estuary–51; Salcombe Harbour–46; Taw/Torridge estuary–49). Fish length ranged from 25.2 to 60 cm (fork length—the length of a fish as measured from the tip of its snout to the fork of the tail), with a mean of 33.5 cm (range: 26–52), 30.9 cm (range: 25.4–38.3) and 30.3 cm (range: 25.2–60) within the Dart estuary, Salcombe harbour and the Taw/Torridge estuaries, respectively (Fig. 4). Of the 146 fish captured, 90% (131 individuals) were less than the Minimum Conversation Reference Size (MCRS; 39.25 cm fork length/42 cm total length), and were therefore assumed to be juvenile or sub-adult fish. The remaining 10% (15 individuals) were above the MCRS, and were assumed to be sexually mature fish. Despite these fish not being immature/juvenile, they were retained for further analysis.

No immediate mortality occurred as a result of the tagging procedure; however, 12 fish were defined as a dead as a result of limited movement within 30 days of release (Fig. S2–supplementary information), these individuals were removed from further analyses. Across all receivers, all remaining tagged fish were detected 5 041 220 times (Dart estuary—1 602 600; Salcombe harbour—2 810 542; and Taw/Torridge estuaries—628 078). The total duration of time individual fish were tracked ranged 0–812 days, with a mean duration of 514 days (range: 124–806) within the Dart, 571 days (range: 0–812) within Salcombe harbour, and 454 days (14–783) within the Taw/Torridge (Fig. 4).

Movement and activity characteristics

Within each Bass Nursery Area (BNA), European bass were detected at every receiver station and were therefore considered to have a cosmopolitan distribution. High variability in fish detections was however detected, which ranged at individual receiver stations from 0.3 ind-^day1 ± 0.03 (SE)–5.9ind-^day1 ± 0.23 (SE) (592–706k total detections) within the Dart, 0.6 ind-^day1 ± 0.04 (SE)–10.3ind-^day1 ± 0.21 (SE) (9 160–616k total detections) within Salcombe harbour, and 0.2 ind-^day1 ± 0.02 (SE)–9.7ind-^day1 ± 0.23 (SE) (6–225k total detections) within the Taw/Torridge. When deployed, receivers in open coastal waters generally recorded lower detections than those deployed within the seaward limit of each site. Within site receivers, demonstrated key activity hotspots occurred at or near the seaward entrance (Fig. 5). In particular, within the Dart and Taw/Torridge specific/individual receivers recorded extremely high numbers of fish detections, suggesting high fish activity within the immediate vicinity of these locations. These receivers accounted for 46.7% of the overall detections within the Dart and 35% within the Taw/Torridge. Within the Dart estuary this high-activity receiver was within the spatial boundaries of the Bass Nursery Area. However, within the Taw/Torridge, the high-activity area was located within the seaward limit of the site but, critically, was outside the spatial boundaries of the Bass Nursery Areas. Within Salcombe harbour high-use areas were recorded at various receivers locations up till ∼4 km of the seaward entrance. All of these locations were within the spatial boundaries of the Bass Nursery Area.

Within each site seasonal trends in water temperature were observed, ranging from 6.6 to 20.1°C. Water temperature was more stable within Salcombe harbour (range: 9.1–19), whereas the Dart (range: 8.3–20.1) and Taw/Torridge estuaries (range: 6.6–19.8) showed greater variability between winter and summer temperatures (Fig. 6). The timing of the Bass Nursery Areas seasonal opening to commercial fishing, occurred when water temperature was at its lowest in all sites (Dart: 8.6–11°C; Salcombe Harbour: 9.2–12.3°C; Taw/Torridge: 6.6–13.1°C) (Fig. 6). Notably, due to the extended period that commercial fishing is permitted within the Taw/Torridge estuary (1^st November–30th April), this covered a broader temperature range than in the Dart estuary and Salcombe harbour.

When modelling the daily presence/absence of tagged European Bass in each site in relation to water temperature, AIC scores indicated inclusion of a site interaction with water temperature significantly improved model performance (Model^{site * temp}: 0 ΔAIC. Model^{site + temp}: 5368ΔAIC. Model^temp:5379 ΔAIC. Model^Site: 9595 ΔAIC. Model^Null: 9604 ΔAIC). Within the Dart estuary, there was a clear positive relationship of higher probability of fish presence as water temperature increased. Within the Taw/Torridge estuaries and Salcombe harbour, this relationship was however less pronounced and/or absent (Table 3, Fig. 6). In both the Taw/Torridge and Salcombe Harbour, there was a high probability of fish presence throughout the year, including periods when commercial fishing is permitted within site boundaries. For example, at the coldest temperatures recorded in each site, the likelihood that European bass would be present was 0.46 (9.1°C) within Salcombe harbour, and 0.57 (6.7°C) within the Taw/Torridge. Within the Dart estuary the equivalent predicted European bass presence/absence was 0.03 (8.6°C) (Table 3, Fig. 6).

Bass nursery area efficacy

The duration of time European bass were actually within the spatial boundaries of a Bass Nursery Area during the time it is protected, was highest within Salcombe Harbour (27.4%) and the Dart estuary (24.4%), and significantly lower within the Taw/Torridge estuaries (1.9%) (Table 4 and Fig. 7). Within the Dart estuary and Salcombe harbour full spatial protection was already achieved, if also introduced to the Taw/Torridge, this would increase the time protected x 7.7 up to 14.7%. Introduction of full temporal closure increased the duration of time European bass would be protected in all sites, though within the Dart and Taw/Torridge this caused a minor increase (Dart: 2% increase, Taw/Torridge: 0.32% increase). The highest protection was achieved by introducing both full spatial and temporal protections across all sites, which would result in European bass being within a protected Bass Nursery Area for 26.5% (Dart), 36.8% (Salcombe Harbour), and 23.8% (Taw/Torridge) of the time.

Discussion

Our data have provided novel insights into the movement and spatial ecology of a high-value species under pressure from overfishing. We have demonstrated, via collection of movement data, boundaries for protected nursery sites did not fully encompass the movement patterns of European bass. Importantly, we were able to assess potential impacts of spatial and temporal refinements to Bass Nursery Area design, which in some sites would have substantial positive impacts on the duration of time fish were actually protected. Further work would be required to better understand how variable protection at critical life stages actually translates to population processes, e.g. mortality, growth and recruitment. The realized impacts of this research are, however, to highlight the critical need for movement data in assessing the relevance of boundaries of protected sites in relation to the movement ecology of the protected species.

Movement characteristics and habitat use

The preservation of estuarine and coastal ecosystems is seen as critical to support population health for estuarine-dependent fish species (Pickett et al. 2004, Childs et al. 2008, Swadling et al. 2022). Therefore, evidence on the spatial and temporal variation in fish distribution within these ecosystems is critical to our understanding, and therefore protection, of key population processes e.g. recruitment. Within the context of this study, European bass are known to exploit estuaries and shallow coastal embayments as nursery (Pickett and Pawson 1994, Stamp et al. 2021) and also as adult feeding locations (Cambie et al. 2016, Doyle et al. 2017). Multiple authors (Doyle et al. 2017; Stamp et al. 2021, Goossens et al. 2024) have highlighted that European bass display high residency and fidelity to coastal sites. A novel finding within the current study includes the telemetry of juvenile and sub-adult fish within designated/protected sites, combined with the presence of activity hot spots at or near the seaward entrances in all sites. Within two of the Bass Nursery Areas included (The Dart and Taw/Torridge), this was particularly acute with limited fish activity seen across the remaining receivers. Whereas in Salcombe harbour (Ria system), high-use areas were distributed across a large extent of the site. Doyle et al. (2017) tracked European bass using acoustic telemetry within Cork Harbour (Ireland), reporting high-use areas were typically in areas with high water flow/fast tidal streams. While not specifically measured in the current study, all high-use areas were also characterized by extreme and rapid water flows which can exceed 3 m s⁻¹ during peak flow. This has been reported for similar species e.g. Spotted Grunter (Pomadasys commersonnii) (Childs et al. 2008) and Australian bass (Macquaria novemaculeata) (Walsh et al. 2012), suggesting shared patterns across a variety of species. Space use for euryhaline species is also likely to be affected by local salinity regimes (Childs et al. 2008). Two of the sites included within the study are dominated by freshwater inputs (The Dart, Taw/Torridge estuaries). Whereas Salcombe harbour is classified as a coastal Ria system in which freshwater input is restricted to a number of small streams (Stamp et al. 2021). It is therefore likely that while European bass can be found throughout coastal sites, high-use areas may be located in areas of relatively stable salinity, high tidal flow and provide suitable feeding e.g. rocky reef or structurally complex and/or vegetated habitat where prey availability is high (Green et al. 2012; Ng et al. 2007).

Efficacy of bass nursery areas

The primary aim of designating Bass Nursery Areas was to improve recruitment i.e. increase survival of juvenile fish (MAFF 1990). However, a major issue with Bass Nursery Areas is that no clear objectives exist for the level of protection that should be provided to juvenile fish i.e. should juvenile fish be protected for 100% of the time? There is also no clear understanding of what level of protection is required to promote/increase recruitment. The results from this study highlight that European bass (>25 cm fork length) actually spend a higher proportion of time within open coastal waters where they are at higher vulnerability to fishing pressure e.g. indiscriminate fishing techniques such as coastal netting, which may reduce survival and recruitment into the adult fishery (Chaves 2022). Despite this, Pickett et al. (2004) reported higher survival of juvenile European bass following designation of Bass Nursery Areas across the UK. Therefore, protection of fish while within semi-enclosed estuarine and coastal sites, albeit on a limited basis, may therefore be sufficient to increase recruitment. Refinements and/or improvements can, however, clearly be made in Bass Nursery Areas which are only partially protected (spatially or temporally), and therefore likely provide minimal protection to the fish they are designed to protect. Furthermore, Pickett et al. (2004) highlighted that juveniles were most likely to recruit as adults into the local area. Therefore, it is possible that by providing full spatial and temporal protection within Bass Nursery Areas, or by layering further local bye-laws which reduce fishing pressure e.g. D&S IFCA netting ban within estuary (D&S IFCA 2018), may result in improved fishing opportunities in open coastal areas adjacent to protected sites.

Spatial management of essential fish habitat

Increasingly, protection of Essential Fish Habitat (EFH) is being incorporated within high-level fisheries management policies and operationalized at local and regional scales for specific species. A good example of which includes, management of Striped bass (Morone saxatilis) fisheries in the USA, a key feature of which is the identification, protection, and preservation of EFH (Ng et al. 2007). These plus additional effort-based restrictions have resulted in large-scale recovery of a once highly depleted fishery (Richards and Rago 1999). Within Europe, specific examples include protection of Black bream (Spondyliosoma cantharus) within specific nesting sites (Davies et al. 2024), or protection of Spiny lobster (Palinurus elephas) populations (Natural England 2024) within Marine Conservation Zones in the UK. Another European example includes, ‘the plaice box’, which was a large area of the southern North Sea, which was identified as important nursery habitat for Plaice (Pleuronectes platessa). Large beam trawlers (>221 kW) were therefore excluded from the area to reduce the incidental capture of undersized fish (Beare et al. 2013). Despite the designation and protection of EFH, the importance of appropriate evaluation frameworks for fisheries management measures remains integral to their success. For example, following the closure of the fishery within the plaice box, juvenile growth rates, biomass and landings across the broader region declined (Beare et al. 2013). Within UK Marine Conservation Zones, limited monitoring occurs to measure the efficacy of designated/protected sites. As also highlighted within the case study included within the current study (European Bass: Bass Nursery Areas) following designation appropriate evaluation frameworks are essential. These should be underpinned by testable objectives that are informed by the best available evidence (Bream et al. 2015). Our data highlight that, within such a framework, it is vital to consider spatiotemporal variation in distribution and habitat use of the relevant species. Finally, it is vital for further studies to identify the realized impacts of spatial protection on population processes e.g. mortality, growth and recruitment (Lees et al. 2021). Description of movement characteristics in relation to management boundaries and environmental conditions is, however, a vital step in understanding the biological and ecological relevance of protected sites to the spatial ecology of mobile animals (Breen et al. 2015, Matley et al. 2022).

Conclusions

Due to technological limitations, the minimum size fish tagged was >25.2 cm fork length. This therefore means that ∼0–3-year fish (Pickett and Pawson 1994) were not included within the study, and the results therefore do not account for the habitat requirements of these ages classes. Future studies should aim to tag and track the full suite of the age classes of the fish which utilize particular sites. This study does, however, demonstrate behavioural ecology of a broad sizes of European bass within coastal and estuarine sites. Spatial management can be used to effectively protect these essential habitats; however, for spatial management policies to be effective, it is crucial that detailed data are collected on the spatial ecologies of the species of concern.

The spatiotemporal limits of these protected sites/BNAs were defined based on best available evidence in 1990 (MAFF 1990). However, since then technological advancements have dramatically increased our understanding of fish spatial ecology (Hussey et al. 2015). Furthermore, dynamic local hydrological conditions influence fish behaviour in unpredictable ways, in particular within highly dynamic coastal systems (Williams et al. 2017), which are also highly influenced by human activity (Whitfield and Elliot 2002) and climate change (Fogarty et al. 2017). Fisheries management should continue to adapt according to the best available evidence of spatiotemporal variation in fish distribution and habitat use, gained e.g. via modern fish tracking techniques, to optimize the environmental, social and economic benefits of using closed areas/spatial management.

Acknowledgements

The authors wish to acknowledge the Devon and Severn Inshore Fisheries and Conservation Authority, Dart Harbour and Navigation Authority, Salcombe Harbour Authority, Sea Jay Live Marine Supplies, North Devon Fishermen’s Association, the Bass Angling Sportsfishing Society and individuals from the commercial and recreational fishing communities for the vital financial and logistical support they provided. Without assistance from these organizations survey work would not have been possible.

Author contributions

All authors contributed equally to the study conception, funding acquisition, survey work, and manuscript writing.

Conflict of interest

None declared.

Data availability

The data underlying this article will be shared on reasonable request to the corresponding author.

References