Key Fisheries Species Research Articles

Decadal changes in biomass and distribution of key fisheries species on Newfoundland's Grand Banks.

Canadian fisheries management has embraced the precautionary approach and the incorporation of ecosystem information into decision-making processes. Accurate estimation of fish stock biomass is crucial for ensuring sustainable exploitation of marine resources. Spatio-temporal models can provide improved indices of biomass as they capture spatial and temporal correlations in data and can account for environmental factors influencing biomass distributions. In this study, we developed a spatio-temporal generalized additive model (st-GAM) to investigate the relationships between bottom temperature, depth, and the biomass of three key fished species on The Grand Banks: snow crab (Chionoecetes opilio), yellowtail flounder (Limanda ferruginea), and Atlantic cod (Gadus morhua). Our findings revealed changes in the centre of gravity of Atlantic cod that could be related to a northern shift of the species within the Grand Banks or to a faster recovery of the 2J3KL stock. Atlantic cod also displayed hyperaggregation behaviour with the species showing a continuous distribution over the Grand Banks when biomass is high. These findings suggest a joint stock assessment between the 2J3KL and 3NO stocks would be advisable. However, barriers may need to be addressed to achieve collaboration between the two distinct regulatory bodies (i.e., DFO and NAFO) in charge of managing the stocks. Snow crab and yellowtail flounder centres of gravity have remained relatively constant over time. We also estimated novel indices of biomass, informed by environmental factors. Our study represents a step towards ecosystem-based fisheries management for the highly dynamic Grand Banks.

Variation in the Physiological Condition of Common Coral Trout (Plectropomus leopardus) Unrelated to Coral Cover on the Great Barrier Reef, Australia

There are a wide variety of fishes that occur exclusively on coral reefs, though it is unclear to what extent these species (especially larger-bodied fisheries target species) are reliant on the specific reef habitat provided by corals. This study explored variation in the physiological condition of common coral trout (Plecropomus leopardus) on Australia’s Great Barrier Reef, explicitly testing whether fish condition varied with local coral cover in the aftermath of severe mass bleaching and coral loss. Both the physiological condition (specifically, the length–weight relationships, hepatocyte vacuolation, and electrical phase angle) of P. leopardus and the live cover of habitat-forming corals varied greatly among the sites considered in this study, but there was little correspondence between these factors. Fish condition was largely influenced by fish size and varied with latitude. While there was no apparent effect of recent coral bleaching and coral loss on the physiological condition of P. leopardus, this does not mean that these key fisheries species will be unaffected by further changes to the environmental conditions and reef habitat. It is important, therefore, that fisheries managers remain vigilant to apparent effects of climate change and other anthropogenic pressures on fisheries stocks.

The socio-economic impact of Marine Protected Areas in Jersey: A fishers’ perspective

Marine Protected Areas (MPAs) are advocated as tools to support sustainable fisheries and biodiversity by excluding the most destructive fishing practices. Some MPAs protect the whole-site of habitat mosaics from bottom-towed fishing but most only restrict damaging activities from specific evidenced conservation features. Social and economic factors influence the success of an MPA but the impact of spatial management changes to local fisheries is rarely captured in post MPA designation monitoring. In Jersey, Channel Islands, two offshore MPAs were designated in 2017 that are managed following the whole-site approach. This study provides an insight into the overall economic importance of key fishery species (whelk (Buccinum undatum), brown crab (Cancer pagurus), scallop (Pecten maximus), lobster (Homarus gammarus), and spider crab (Maja brachydactyla) to local fishing fleets and the impact of the MPAs on local, small-scale fishers in Jersey. Total landings (kg and £) in Jersey pre and post MPA designation were calculated from logbook and primary sales data and a structured interview was developed and tested as a research tool to document the impact (positive and negative) of the MPA designation on local fishers. Specific questions were designed to elicit both quantitative and qualitative data relating to the participants (n = 21) fishing activity; support for the MPAs; income and job satisfaction; subjective well-being and current sales strategies. The results demonstrate that one mobile gear vessel respondent was displaced from traditional fishing grounds as a result of the MPA designation. Fishers also reported an increase in static fishing inside the MPAs, post designation. Generally, there are high levels of support for the MPA from static fleet respondents. In the first year since designation there have been no reported changes to catch (kg, £). Mobile gear fishers reported a lower subjective wellbeing and satisfaction with their job and income than static gear fishers, despite greater profits. The major concern reported by the mobile fleet that contributed to their stress levels, was not attributed to the MPA designations but related to conflict with French static net fisheries operating outside of the MPAs. Ongoing support for Jersey’s fishers and securing a sustainable and fulfilling livelihood will require further spatial management of fisheries outside of the MPAs with a possibility of setting gear or effort limits on static fishereis within the MPAs.

Benefits of measurable population connectivity metrics for area-based marine management

The dispersal of larvae by ocean currents is likely to represent an increasingly important driver of marine population dynamics across fragmented habitats. A boost in availability of larval dispersal data from biophysical simulations has therefore led to routine calculations of population connectivity metrics that are used for area-based management decision support, including the placement of Marine Protected Areas (MPAs). However, connectivity-based decision support for area-based management is often complex, highly uncertain, and the associated conservation impact rarely if ever evaluated. In combination, these challenges risk stakeholder engagement, compliance, and overall management effectiveness. Here we use a case study representing multiple key fishery species on coral reefs in Indonesia to demonstrate that consideration of larval dispersal for MPA placement decision support could be critical to recover both fish populations and fisheries from depletion, thereby mitigating potentially severe impacts on coastal communities. Importantly, we further show that MPA placement decisions can be effective even if based on comparatively simple and empirically measurable dispersal characteristics. Maximizing larval export, expressed as the contribution of larvae from MPA candidate sites to total larval settlement in surrounding areas, for example, was found to be a broadly beneficial MPA placement prioritization approach. Across investigated fish families with diverse life histories, this strategy resulted in MPA network designs that increased catches by a factor of 1.3 ± 0.3 (mean ± SD) and total fish biomass by a factor of 3.2 ± 0.3 (9.7 ± 1.2 in no-fishing areas and 1.4 ± 0.3 in fished areas) compared to conditions without effectively managed or protected areas. Our findings are relevant for both the implementation and impact evaluation of global marine conservation policies, specifically in tropical biodiversity hotspots, such as Indonesia, where coral reefs are often overfished and increasingly threatened but local communities highly dependent on sustainable fisheries.

Evaluating the Feasibility of Sustainable Seafood Labelling Programmes in Small Island Developing States: A Pilot Study of Artisanal Fisheries in Seychelles

The Republic of Seychelles is one of six African Small Island Developing States (SIDS) and has a marine-based economy reliant on fisheries and international tourism. Seychelles has been flagged by the United Nations as highly vulnerable to climate change. Climatic threats are compounded with population declines of key fishery species. A progressive national stance towards ocean sustainability and an emerging economy partially driven by tourists are two of several factors that make Seychelles a good candidate for a sustainable seafood labelling and consumption programme, which would provide market-based incentives for fishery harvesters, regulators, buyers and consumers to improve sustainable practices. To address the feasibility of such a programme, we conducted a pilot study, surveying 33 artisanal fishers and mapping supply chain structure to examine incentives and challenges. Questions addressed fishers’ years of experience, reliance on fishing for income, and flexibility in gear type and species targeted. Of the total number of respondents, 64% would like to see a programme implemented but only 34% thought it would be successful. Participants identified several barriers and benefits that primarily spanned socioeconomic and regulatory themes. Our pilot results indicate the sociocultural and economic impacts of sustainability programmes in Seychelles are as important as environmental considerations, a finding pertinent to anyone undertaking similar research efforts in other SIDS. We advocate for the necessity of thorough, location-based research and in-depth stakeholder consultation to elucidate economic, societal, behavioural and cultural factors that will affect the success of designing and implementing seafood labelling programmes in SIDS.

Saltmarsh grass supports fishery food webs in subtropical Australian estuaries

All fishery food webs are ultimately underpinned by organic matter produced by algae and plants, some of it supplied by primary producers at the fringes of fish habitats. This is no different in tropical and subtropical estuaries where secondary production by crustaceans and finfish may depend on coastal wetlands (e.g. mangroves, seagrass, saltmarshes) abutting channels. Coastal urbanisation is a major cause of wetland loss globally. Hypothetically, reduced wetland area may propagate to less fisheries production if wetland contributions to food webs are substantial – this is the prime question addressed here. We sampled key fisheries species in subtropical estuaries in reaches of moderate urbanisation (18–33% of shoreline hardened) and in reference locations dominated by wetlands, on the east coast of Australia. We used triple stable isotopes (C, N, S) to estimate (using mixing models) the trophic contributions of the key primary producers to regional fisheries species. Organic matter from wetland plants, particularly saltmarsh grass (Sporobolus virginicus), underpinned fishery food webs in most cases (with median contributions ranging from 18 to 88% for saltmarsh grass, followed by 6–70% for C3 wetland plants (e.g. mangroves, phragmites) and 3–36% by benthic algae). Moderate levels of urban transformation of estuarine margins did not change the dominance of wetland carbon for fish and crustaceans in settings without significant seagrass meadows. Given the demonstrated importance of saltmarshes, and other coastal wetlands, to regional fisheries production, conservation of these habitats is necessary in the face of multiple anthropogenic threats.

Habitat complexity influences the structure of food webs in Great Barrier Reef seagrass meadows

AbstractStructural habitat complexity is a fundamental attribute influencing ecological food webs. Simplification of complex habitats occurs due to both natural and anthropogenic pressures that can alter productivity of food webs. Relationships between food web structure and habitat complexity may be influenced by multiple mechanisms, and untangling these can be challenging. We investigated whether (1) size spectra vary across a gradient of habitat complexity in seagrass meadows and (2) structural complexity changes the importance of different primary producers supporting the food web (determined using stable isotope analysis) in the Great Barrier Reef World Heritage Area. We found that moderately complex meadows had much steeper size spectra slopes, caused by a higher abundance of smaller animals and fewer larger animals, while meadows on either end of the complexity scale (low and a single meadow with very high complexity) had shallower slopes, indicative of a more balanced distribution of animal sizes across the spectrum. We also found that the importance of epiphytic algae as a food source was high in most meadows, despite the increase in seagrass surface area on which epiphytes could grow. The consistent importance of epiphytic algae suggests that the changes in the availability of different potential food sources did not affect food web structure. Our findings indicate that food web structure may change with variations in structural complexity because of changes in the abundance of smaller and/or larger animals. Food web structure and food sources are important determinants of the dynamic stability of food webs. Size spectra analysis is already used as a monitoring tool for assessing populations of key fisheries species in commercial fishing operations, and thus, we recommend using size spectra as a proxy for assessing the structure of the food webs in different types of seagrass meadows. Size spectra may be a useful indicator of how different meadows provide for ecosystem services such as fisheries.

Social Dimensions of Resilience in Social-Ecological Systems

Resilience is generally considered the capacity to tolerate, absorb, cope with, and adjust to changing social or environmental conditions while retaining key elements of structure, function, and identity. The social dimensions of resilience are vital to understanding the impacts of environmental changes, such as climate change, on social-ecological systems. In this Primer, we introduce key social factors that provide resilience in linked social-ecological systems, including (1) assets, (2) flexibility, (3) social organization, (4) learning, (5) socio-cognitive constructs, and (6) agency. Emerging frontiers of resilience include applying social-ecological network approaches, investigating power relations, and exploring how transformative versus adaptive changes can promote resilience. A further understanding of the social dimensions of social-ecological systems can provide valuable information on how these systems may respond to change and equip us with the knowledge to support or build resilience in vulnerable systems.

From data compilation to model validation: a comprehensive analysis of a full deep-sea ecosystem model of the Chatham Rise

The Chatham Rise is a highly productive deep-sea ecosystem that supports numerous substantial commercial fisheries, and is a likely candidate for an ecosystem based approach to fisheries management in New Zealand. We present the first end-to-end ecosystem model of the Chatham Rise, which is also to the best of our knowledge, the first end-to-end ecosystem model of any deep-sea ecosystem. We describe the process of data compilation through to model validation and analyse the importance of knowledge gaps with respect to model dynamics and results. The model produces very similar results to fisheries stock assessment models for key fisheries species, and the population dynamics and system interactions are realistic. Confidence intervals based on bootstrapping oceanographic variables are produced. The model components that have knowledge gaps and are most likely to influence model results were oceanographic variables, and the aggregate species groups ‘seabird’ and ‘cetacean other’. We recommend applications of the model, such as forecasting biomasses under various fishing regimes, include alternatives that vary these components.

Implications of a climate-induced recruitment shift in the stock assessment of Patagonian grenadier (Macruronus magellanicus) in Chile

Patagonian grenadier (Macruronus magellanicus) is the most abundant demersal fisheries resource off Chilean Patagonia, and also is a key fisheries species off the south of Argentina and off the Falkland Islands. A Stock Synthesis assessment shows that this stock has declined in abundance off Chile, which has been attributed to a major change in recruitment strength, and subsequent production, after 1999. An assessment is conducted in which the change in recruitment is modelled as a shift in the stock-recruitment relationship. Management Strategy Evaluation is then used to examine the consequences of a mis-match between the assumptions related to recruitment in the assessment used to set the annual total allowable catch (TAC), and those in the operating model that represents the actual situation being managed. A management strategy that does not consider a shift in recruitment resulted in average TAC values of approximately 125,000 t, substantially larger than the sustainable yield of 45,000 t when there is a recruitment shift. A management strategy based on ignoring the shift in recruitment would thus lead to unsustainable catches, with major impacts on the ecosystem as well as the industry and coastal communities reliant on the fishery, if there was an actual shift in recruitment. Management of the fishery has not accounted for a recruitment shift, and annual landings have been consistently lower than the estimated annual TACs. The 2014 landings are similar to the long term TAC estimated by the assessment models under the Shift operating model. The history of the Patagonian grenadier fishery demonstrates the benefits of taking a precautionary approach that accounts for changes in fish productivity (whether climate-driven or otherwise). However, there can be considerable delays before a shift is observed in recruitment estimates or assessment model mis-specification is detected. The need for alternative approaches for providing more timely recruitment information is discussed.

Biology, ecology and biogeography of the South American silver croaker, an important Neotropical fish species in South America

The South American silver croaker is a popular fish that has recently received substantial attention from scientists, mainly due to its importance as source of animal protein and as a key fisheries species. However, little is known about the conditions that explain its historical and current spatial distribution, both in its native habitat and where it is a successful invasive species. The aim of the present study was to explore the ecological information available for this species, to then critically examine ecological theories related to the conditions underpinning its success. To this end, an exhaustive literature search was conducted with the immediate aim of investigating whether the success of South American silver croaker was driven by species-climate or species–human interactions. The non-native populations were found to occupy climate niche spaces different from those observed in their native ranges. In addition, it was clear that humans played a role in facilitating the large-scale dispersion of silver croaker, and assisted as agents of impact driving the observed current and, probably, the future spatial distribution, which we can predict from our data and from the pattern of propagule pressure. Overall, the current biogeography of this species illustrates how the construction of dams, along with the introduction and stocking of non-native species, overfishing and other human activities can alter fish populations and assemblages. Such processes can reduce native species, increase the abundance and distribution of invasive species, as well as cause changes in life-history traits and genetic variability, all with long-term socioeconomic consequences.

Molecular Plasticity under Ocean Warming: Proteomics and Fitness Data Provides Clues for a Better Understanding of the Thermal Tolerance in Fish.

Ocean warming is known to alter the performance and fitness of marine organisms albeit the proteome underpinnings of species thermal tolerance are still largely unknown. In this 1-month experiment we assessed the vulnerability of the gilt-head sea bream Sparus aurata, taken here as a biological model for some key fisheries species, to ocean warming (control 18°C, nursery ground temperature 24°C and heat wave 30°C). Survival was impaired after 28 days, mainly at 30°C although fishes' condition was unaltered. Muscle proteome modulation was assessed at 14 and 21 days, showing that protein expression profiles were similar between fish exposed to 18 and 24°C, differing from fish exposed to 30°C. Fish subjected to 24°C showed an enhanced glycolytic potential and decreased glycogenolysis mainly at 14 days of exposure. Fish subjected to 30°C also showed enhanced glycolytic potential and up-regulated proteins related to gene expression, cellular stress response (CSR), and homeostasis (mostly cytoskeletal dynamics, acid-base balance, chaperoning). However, inflammatory processes were elicited at 21 days along with a down-regulation of the tricarboxylic acid cycle. Thus, juvenile fish seem able to acclimate to 24°C but possibly not to 30°C, which is the predicted temperature for estuaries during heat waves by the year 2100. This may be related with increasing constraints on organism physiology associated with metabolic scope available for performance and fitness at higher temperatures. Consequently, recruitment of commercial sea breams may be in jeopardy, highlighting the need for improved management plans for fish stocks.

The utility of bioenergetics modelling in quantifying predation rates of marine apex predators: Ecological and fisheries implications

Predators play a crucial role in the structure and function of ecosystems. However, the magnitude of this role is often unclear, particularly for large marine predators, as predation rates are difficult to measure directly. If relevant biotic and abiotic parameters can be obtained, then bioenergetics modelling offers an alternative approach to estimating predation rates, and can provide new insights into ecological processes. We integrate demographic and ecological data for a marine apex predator, the broadnose sevengill shark Notorynchus cepedianus, with energetics data from the literature, to construct a bioenergetics model to quantify predation rates on key fisheries species in Norfolk Bay, Australia. We account for the uncertainty in model parameters by incorporating parameter confidence through Monte Carlo simulations and running alternative variants of the model. Model and parameter variants provide alternative estimates of predation rates. Our simplest model estimates that ca. 1130 ± 137 N. cepedianus individuals consume 11,379 (95% CI: 11,111–11,648) gummy sharks Mustelus antarcticus (~21 tonnes) over a 36-week period in Norfolk Bay, which represents a considerable contribution to total predation mortality on this key fishery species. This study demonstrates how the integration of ecology and fisheries science can provide information for ecosystem and fisheries management.

Decrease in young-of-the-year yellow perch growth rates following Bythotrephes longimanus invasion

Bythotrephes longimanus, an invasive zooplankter from Eurasia, has caused severe declines in native zooplankton communities in Rainy and Kabetogama lakes in northern Minnesota. Both lakes have experienced a 40–60% decrease in peak summer zooplankton biomass following B. longimanus establishment around 2006–2007. In these lakes, yellow perch (Perca flavescens) are a key fishery species, and young-of-the-year (YOY) yellow perch are mainly planktivorous during their first summer. This led to concern that their growth could be detrimentally affected by the depletion of zooplankton forage. We used seining data to compare growth rates of YOY yellow perch before (2001–2005) and after (2008–2012) B. longimanus establishment in Rainy and Kabetogama lakes. Nearby Lake Vermilion, assumed to have been unaffected by B. longimanus during this time period, was used as a reference for natural variation in YOY growth in the region. YOY yellow perch length was modeled as a linear function of cumulative growing degree days (GDD) throughout the summer, and the slope of the relationship was compared between pre- and post-B. longimanus time periods for the three study lakes. The two lakes with B. longimanus showed similar decreases in YOY yellow perch growth rate relative to GDD, whereas Lake Vermilion showed no evidence of a decline in growth rates during this period. The reduction in growth rates resulted in an approximate 10% decrease in mean length of YOY yellow perch at the end of the summer after B. longimanus establishment, which could lead to further effects of this invasive zooplankter at higher trophic levels.

Ocean warming alters cellular metabolism and induces mortality in fish early life stages: A proteomic approach

Climate change has pervasive effects on marine ecosystems, altering biodiversity patterns, abundance and distribution of species, biological interactions, phenology, and organisms’ physiology, performance and fitness. Fish early life stages have narrow thermal windows and are thus more vulnerable to further changes in water temperature. The aim of this study was to address the sensitivity and underlying molecular changes of larvae of a key fisheries species, the sea bream Sparus aurata, towards ocean warming. Larvae were exposed to three temperatures: 18°C (control), 24°C (warm) and 30°C (heat wave) for seven days. At the end of the assay, i) survival curves were plotted for each temperature treatment and ii) entire larvae were collected for proteomic analysis via 2D gel electrophoresis, image analysis and mass spectrometry. Survival decreased with increasing temperature, with no larvae surviving at 30°C. Therefore, proteomic analysis was only carried out for 18°C and 24°C. Larvae up-regulated protein folding and degradation, cytoskeletal re-organization, transcriptional regulation and the growth hormone while mostly down-regulating cargo transporting and porphyrin metabolism upon exposure to heat stress. No changes were detected in proteins related to energetic metabolism suggesting that larval fish may not have the energetic plasticity needed to sustain cellular protection in the long-term. These results indicate that despite proteome modulation, S. aurata larvae do not seem able to fully acclimate to higher temperatures as shown by the low survival rates. Consequently, elevated temperatures seem to have bottleneck effects during fish early life stages, and future ocean warming can potentially compromise recruitment’s success of key fisheries species.

Climate change implications for Torres Strait fisheries: assessing vulnerability to inform adaptation

Climate change impacts on marine fisheries are being observed in tropical regions, including northern Australia and the Pacific. In the Torres Strait, Islanders have a long association with their sea country that holds significant cultural, social and economic importance. Future impacts of climate change on marine fisheries stocks and supporting habitats will affect Torres Strait Islander communities. We assessed the relative vulnerability of 15 key fishery species in Torres Strait using a semi-quantitative framework modified from the Intergovernmental Panel on Climate Change that integrated both ecological and social indicators of exposure, sensitivity and adaptive capacity. The assessment identified species with high, medium and low vulnerability to projected climate change in 2030. The species assessed as having the highest vulnerability were: Holothuria whitmaei (black teatfish), Pinctada margaritifera (black-lipped pearl oyster), Dugong dugon (dugong), and Trochus niloticus (trochus). A separate prioritisation process that considered the cultural and economic value of species identified three high priority species for future management focus: D. dugon, marine turtles (principally Chelonia mydas) and Panulirus ornatus (tropical rock lobster). These results can inform fishers and managers to prepare for the effects of climate change and minimise impacts. The relatively healthy condition of most fisheries in the Torres Strait is likely to assist successful adaptation.

Age and growth of sharptooth catfish, Clarias gariepinus (Burchell, 1822) (Clariidae), in the Lower Okavango Delta, Botswana

Managing any inland fishery requires reliable age data and accurate estimates of growth rate. Clarias gariepinus, the largest catfish species in most tropical African floodplain river systems, is an important constituent of subsistence fishery catches. We used otolith-derived age estimates to describe patterns of age and growth for C. gariepinus from the Lower Okavango Delta in northern Botswana. Edge analysis of sectioned sagittal otoliths showed that growth zone deposition occurred during the annual flood peak between July and September. The maximum recorded age was 8 years. Growth was best described by the von Bertalanffy Growth Model of the form E[L|age] = 528.70(1–e–0.72(age+1.35)). A comparison of growth parameters from this study with those from previous studies suggests two distinct populations of C. gariepinus between the Upper and Lower Okavango Delta, emphasising the importance of regional stock assessment for key fishery species. The fairly short life span and high variability in growth of C. gariepinus are important indicators that it is imperative to maintain natural habitat and flow regime for sustainable management of fishery resources in the Lower Okavango Delta.

Participatory Fishing Community Assessments to Support Coral Reef Fisheries Comanagement

Comanagement of natural resources involves shared management authority and responsibility between resource users or community groups at local levels and central government authorities. In data-poor, small-scale fisheries systems, community-based planning efforts can be informed by participatory research approaches that involve community members and stakeholder groups in the design, development, and implementation of research. This article draws upon research in Maunalua Bay, O'ahu , Hawai'i, to illustrate the utility of participatory assessments in communities, institutions, and organizations as they transition toward comanagement arrangements. A community-led survey effort revealed temporal changes in habitat use patterns and declines in key fisheries species and habitats. Fishing activities in Maunalua Bay are primarily noncommercial in nature and many of the direct benefits from local fisheries are distributed through social-kinship networks. The fishing community exhibited a high capacity for engagement in community-based planning efforts and also provided input on proposed management measures. The article concludes by documenting the social and environmental factors that influence the distribution of coral reef fisheries ecosystem services, and assessing sliding baselines among community fishers. Participatory resource assessments hold promise for building local social adaptive capacity, bringing together disparate stakeholder groups, and building place-based natural resource management plans reflective of local contexts and community priorities.

Genetic connectivity and diversity of walleye (Sander vitreus) spawning groups in the Huron–Erie Corridor

The Huron–Erie Corridor (HEC) connects the upper and lower Great Lakes, providing key fish passage. A century of channelization, dredging, and pollution has led to habitat loss and declining fish numbers. Since 2004, the multi-agency HEC initiative augmented fish spawning habitat at Belle Isle and Fighting Island in the Detroit River, whose populations are examined here. We analyze genetic patterns among seven spawning groups (N=311) of walleye Sander vitreus, a key fishery species, using nine nuclear DNA microsatellite loci and mitochondrial DNA control region sequences. Results reveal that all spawning groups contained appreciable genetic diversity (microsatellites: HO=0.72; mtDNA: HD=0.73) and showed a mixture of connectivity and divergence. Genetic relationships did not fit an isolation by geographic distance hypothesis, with some closely spaced populations being very different. Notably, the Flint River–Lake Huron spawning group was the most divergent, showing no genetic exchange. The Belle Isle and Fighting Island populations markedly differed, with the latter showing some genetic exchange with the Grosse Ile (Detroit River) and the Huron River (northwest Lake Erie) populations to the south. Walleye spawning at Fighting Island experienced no significant change in overall genetic diversity pre- versus post-habitat augmentation, but the allelic frequency changed. Our results comprise an important baseline for future population analyses and habitat assessment of these habitat augmentation areas. Despite habitat degradation and pollution, it appears that historic walleye spawning groups have persisted along the HEC, meriting continued genetic monitoring and further restoration efforts to conserve and enhance this important and diverse fishery.

Putting marine sanctuaries into context: a comparison of estuary fish assemblages over multiple levels of protection and modification

Abstract In recent decades there has been a significant effort to establish marine sanctuaries for the purpose of protecting marine biodiversity and ecological processes. While many studies have demonstrated that marine sanctuaries increase the abundance, diversity, and trophic level of marine fish communities, few have compared these parameters across multiple levels of protection and human modification. This study utilized baited remote underwater video to compare fish assemblages between marine parks, between different levels of protection within parks (sanctuary and habitat protection zones), and between parks and highly modified systems with similar ecological communities. It was demonstrated that sanctuary zones have higher abundance of targeted fish species compared with other areas within some marine parks. The total abundance of targeted species and abundances of some key fisheries species (e.g. pink snapper) were found to be higher in sanctuary zones. This suggests that increased protection may be effective at improving these aspects of the fish assemblage. However, when marine parks were compared with highly modified environments it was found that targeted species were much more abundant in the highly modified systems. Community composition of entire fish assemblages also differed between these levels of modification and economically important fisheries species contributed most to this difference. These findings suggest that while highly protected sanctuary zones may increase the abundance of targeted fish compared with less protected areas within the same estuary, highly industrialized or urbanized systems, not typically chosen as marine parks, may actually support more targeted species of fish. It was demonstrated that forms of modification in addition to fishing pressure are having large effects on fish assemblages and productivity. Copyright © 2011 John Wiley & Sons, Ltd.