Effects of habitat structural complexity on nekton assemblages: lab and field observations in southern Louisiana

Greater structural complexity is often associated with more diverse and abundant species assemblages. Biogenic reefs formed by the eastern oyster (Crassostrea virginica) are structurally complex in nature and have been recognized for their potential habitat value in estuarine systems along the Atlantic and Gulf of Mexico coasts. To determine how the structural complexity of newly created oyster reefs may influence the abundance and distribution of species, three objectives were established. First, to examine spatial and temporal patterns of nekton use at newly created oyster reefs, as well as the impact of wave exposure, six paired oyster reef and mud-bottom treatments at low and medium wave energy shorelines were sampled quarterly, from June 2009 to March 2010, at Caillou (Sister) Lake, Louisiana, using gill nets, seine, and substrate trays. Transient species showed seasonal shifts with no evidence of habitat preference. Resident species were consistently more abundant at oyster reefs than mud-bottom treatments. There were no patterns in nekton use that could be directly attributed to wave exposure. Second, to determine how changes within the structural complexity of newly created oyster reefs may influence nekton use, oyster reef treatments of various complexities were created and sampled using a drop sampler. The presence of oyster reefs per se was the most important factor determining nekton assemblages; newly created oyster reefs provided habitat for nekton assemblages, but there was little difference between reef treatments. Lastly, to determine how oyster reefs mediate predator foraging success, treatments of various complexities were created and trials executed in a laboratory setting using wild red drum (Scianops occelatus) and grass shrimp (Palaemonetes pugio). Foraging success was negatively correlated to the structural complexity of oyster reefs, indicating there may be a point above which increased complexity no longer increases the refuge value of the reef. These results show that oyster reefs may support a high abundance and diversity of resident nekton, but that after structure is introduced, further increasing structural complexity does not automatically increase species abundance and diversity, or the amount of refugia provided

Oyster Reef Restoration Supports Increased Nekton Biomass and Potential Commercial Fishery Value

Across the globe, discussions centered on the value of nature drive many conservation and restoration decisions. As a result, justification for management activities increasingly asks for two lines of evidence: (1) biological proof of augmented ecosystem function or service, and (2) monetary valuation of these services. For oyster reefs, which have seen significant global declines and increasing restoration work, the need to provide both biological and monetary evidence of reef services on a local-level has become more critical in a time of declining resources. Here, we quantified species biomass and potential commercial value of nekton collected from restored oyster (Crassostrea virginica) reefs in coastal Louisiana over a 3-year period, providing multiple snapshots of biomass support over time. Overall, and with little change over time, fish and invertebrate biomass is 212% greater at restored oyster reefs than mud-bottom, or 0.12 kg m−2. The additional biomass of commercial species is equivalent to an increase of local fisheries value by 226%, or $0.09 m−2. Understanding the ecosystem value of restoration projects, and how they interact with regional management priorities, is critical to inform local decision-making and provide testable predictions. Quantitative estimates of potential commercial fisheries enhancement by oyster reef restoration such as this one can be used directly by local managers to determine the expected return on investment

Nutrient capture and sustainable yield maximized by a gear modification in artisanal fishing traps

Coral reef artisanal fisheries are an important source of nutrition and economic wellbeing for coastal communities, but their management is subject to conflicts and tradeoffs between short-term food security benefits and long-term ecological function. One potential tradeoff is between nutrient capture and fish yields, where targeting small, nutrient-dense species may be more valuable for food security than maximizing fish yields, which is more closely aligned with supporting biodiversity and ecological function. We explored these potential tradeoffs by comparing two similar gears: traditional African basket traps and traps modified with an escape gap. Traps without escape gaps captured a higher frequency of fish with body sizes below their estimated lengths at maximum sustainable yield than gated traps. Estimates of nutrient yields for six micronutrients among the 208 captured species indicated high hump-shaped relationships for gated traps and low and linear positive relationships for traditional traps. Maximum nutrients in gated traps frequently corresponded to body sizes at maximum sustainable yield. Daily capture rates of nutrients were above daily needs more often in gated than traditional traps, but calcium values were low in both trap designs. Gated traps were more likely to capture species with unique and potentially important functional traits, including browsing herbivores, which could have negative effects on ecological functions and reef recovery. However, gated traps also catch fewer immature fish and fewer predators. Our results indicate that nutrient yields can be maximized while using a gear that captures larger and more sustainable body sizes in coral reef artisanal fisheries. Preferential targeting of nutrient-dense fishes is only one of many metrics for evaluating a nutrition-centered management strategy and may only be a management target in specific contexts

Identifying hotspots for spatial management of the Indonesian deep-slope demersal fishery

The Indonesian deep-slope demersal fishery targets mostly snappers and groupers and is vital for the wellbeing of millions of people. More than 100 species are captured at depths of 50–500 m along shelves and seamounts using mostly droplines and bottom longlines. The main target species are Pristipomoides multidens, Pristipomoides filamentosus, Pristipomoides typus, Atrobucca brevis, Epinephelus areolatus, and Lutjanus malabaricus. The fleet in this fishery is predominantly unlicensed small-scale (1–10 gross ton) vessels. The fishery is unmanaged and lacks data that would allow policymakers to formulate sustainable management strategies. Here, we use fisheries-dependent data on catch composition, as well as fishing location and gear type, to determine factors that dictate catch composition and catches containing high proportions of immature fishes. Results indicate that immature fish assemblages are caught in particular locations, or “hotspots,” through a combination of fishing gear and habitat characteristics. The important “hotspots” occurred in the Java Sea-Makassar Strait area. Only 2.4% of marine protected areas (MPAs) were located within “hotspots.” Our findings highlight places of high conservation priority, such as the Java Sea, where expansion of current MPAs would greatly benefit the deep-slope demersal fishery in Indonesia by reducing immature catches, thus identifying a preexisting management that is appropriate for the sustainability of this fishery. The modeling methods we developed are transferable to other fisheries that lack data on fish abundance in order to prioritize management and conservation

A crew-operated data recording system for length-based stock assessment of Indonesia’s deep demersal fisheries

Deep demersal fisheries in Indonesia yielded close to 90,000 metric tons of snapper and grouper in 2019, landed by a fleet of approximately 10,000 fishing boats. Prior to the present study, information on these multi-species, dispersed, small- to medium-scale fisheries was scarce, while reliable species-specific data on catch and effort were non-existent. This data-deficiency made stock assessments and design of harvest control rules impossible. We developed a new data collection method, the Crew Operated Data Recording System (CODRS), to collect verifiable species- and length-composition data from catches across all segments of the fleet. CODRS engaged crews of 579 fishing vessels to take pictures of each fish in their catch, in combination with the deployment of a tracking device on their boats. Furthermore, we also conducted a frame survey to map the fleet across the entire Indonesian archipelago. Using more than 2 million CODRS images, we aimed to understand the basic characteristics and challenges within the fishery. We updated life-history parameters for the top 50 species in the fishery based on the maximum observed length-frequency distribution of the catch (i.e., asymptotic length, size at maturity, optimum fishing length, total mortality, and spawning potential ratio). Length-based stock assessments using the updated life-history parameters showed high risks of overfishing for most of the major target species, especially for snapper species with large maximum sizes. Our results indicated that effective management and harvest strategies are urgently needed across Indonesia’s eleven Fishery Management Areas to prevent the collapse of these important fisheries

Using Seafood Traceability to Teach the Complexities of Natural Resource Management and Sustainability

This lesson plan addresses the challenge of conveying to students the globalized nature and complexity of natural resource management. Specifically, it uses seafood traceability, or the ability to track seafood as it moves through the global seafood supply chain, as a theme for understanding the potential for science and technological innovations to enable traceability as well as the different roles that various stakeholders play in ensuring fisheries sustainability. The lesson plan conveys several themes related to environmental sustainability including: the role of consumer empowerment, the importance of data and information sharing, the need to coordinate multiple stakeholders, and the intersection of science, technology, and policy- making. In one classroom activity, students are guided through a small-group, active-learning exercise that challenges them to make sustainable seafood choices from a restaurant menu. In another activity, students are asked to role-play and consider the information needs of various stakeholders in the seafood supply chain. Overall, the lesson plan is designed to demonstrate that there is no one single solution to realize seafood traceability and ensure fisheries sustainability. Instead, fisheries and natural resource management require multifaceted solutions and the involvement of multiple sectors of society

Establishing an Anthropogenic Nitrogen Baseline Using Native American Shell Middens

Narragansett Bay, Rhode Island, has been heavily influenced by anthropogenic nutrients for more than 200 years. Recent efforts to improve water quality have cut sewage nitrogen (N) loads to this point source estuary by more than half. Given that the bay has been heavily fertilized for longer than monitoring programs have been in place, we sought additional insight into how N dynamics in the system have historically changed. To do this, we measured the N stable isotope (δ15N) values in clam shells from as early as 3000 BP to the present. Samples from Native American middens were compared with those collected locally from museums, an archeological company, and graduate student thesis projects, during a range of time periods. Overall, δ15N values in clam shells from Narragansett Bay have increased significantly over time, reflecting known patterns of anthropogenic nutrient enrichment. Pre-colonization midden shell δ15N values were significantly lower than those post-European contact. While there were no statistical differences among shells dated from the late fifteenth century to 2005, there was a significant difference between 2005 and 2015 shells, which we attribute to the higher δ15N values in the effluent associated with recent sewage treatment upgrades. In contrast, the δ15N values of shells from the southern Rhode Island coast remained constant through time; while influenced by human activities, these areas are not directly influenced by point-source sewage discharge. Overall, our results show that this isotope technique for measuring δ15N values in clam shells provides useful insight into how N dynamics in coastal ecosystems have changed during thousands of years, providing managers vital historical information when setting goals for N reduction

Oyster Reefs in Northern Gulf of Mexico Estuaries Harbor Diverse Fish and Decapod Crustacean Assemblages: A Meta-Synthesis

Oyster reefs provide habitat for numerous fish and decapod crustacean species that mediate ecosystem functioning and support vibrant fisheries. Recent focus on the restoration of eastern oyster (Crassostrea virginica) reefs stems from this role as a critical ecosystem engineer. Within the shallow estuaries of the northern Gulf of Mexico (nGoM), the eastern oyster is the dominant reef building organism. This study synthesizes data on fish and decapod crustacean occupancy of oyster reefs across nGoM with the goal of providing management and restoration benchmarks, something that is currently lacking for the region. Relevant data from 23 studies were identified, representing data from all five U.S. nGoM states over the last 28 years. Cumulatively, these studies documented over 120,000 individuals from 115 fish and 41 decapod crustacean species. Densities as high as 2,800 ind m−2 were reported, with individual reef assemblages composed of as many as 52 species. Small, cryptic organisms that occupy interstitial spaces within the reefs, and sampled using trays, were found at an average density of 647 and 20 ind m−2 for decapod crustaceans and fishes, respectively. Both groups of organisms were comprised, on average, of 8 species. Larger-bodied fishes captured adjacent to the reef using gill nets were found at an average density of 6 ind m−2, which came from 23 species. Decapod crustaceans sampled with gill nets had a much lower average density, \u3c1 ind m−2, and only contained 2 species. On average, seines captured the greatest number of fish species (n = 33), which were made up of both facultative residents and transients. These data provide general gear-specific benchmarks, based on values currently found in the region, to assist managers in assessing nekton occupancy of oyster reefs, and assessing trends or changes in status of oyster reef associated nekton support. More explicit reef descriptions (e.g., rugosity, height, area, adjacent habitat) would allow for more precise benchmarks as these factors are important in determining nekton assemblages, and sampling efficiency

Vulnerability of Resource Users in Louisiana’s Oyster Fishery to Environmental Hazards

Knowledge of vulnerability provides the foundation for developing actions that minimize impacts on people while maximizing the sustainability of ecosystem goods and services. As a result, it is becoming increasingly important to determine how resource-dependent people are vulnerable to environmental hazards. This idea is particularly true in coastal Louisiana, USA, where the current era of rapid land loss has the potential to undermine oyster fisheries. However, little is known about how such environmental change might differentially affect resource users and stakeholders. We examined social components of vulnerability to environmental hazards using indicators of susceptibility and adaptive capacity within the oyster fishery of Terrebonne Parish, Louisiana. Specifically, we used structured interviews to compare three resource-user roles: oyster fishers, oyster fishers/lease owners, and oyster lease owners only. Results indicated that oyster fishers/lease owners were highly dependent and thus susceptible to changes in the fishery because of high levels of occupational identity. These same people, however, were the most adaptable to change, which was reflected in their willingness to learn about new practices and evolve over time. Higher susceptibility in this group was offset by an increased ability to adapt, cope, and respond to changes in the environment. In contrast to these findings, oyster fishers that did not own any portion of a lease or business in which they operated were bad at coping with change and frequently held negative or fatalistic views on financial planning. These attributes made them the most vulnerable to environmental hazards. Overall, the most vulnerable participants in the Terrebonne Parish oyster fishery were those with low to moderate levels of personal and financial buffers and trust, coupled with high occupational identity and a low motivation to change. Local policy actions that target these attributes are likely to be the best entry points to reducing the vulnerability of stakeholders to hazards

Catch Composition and Selectivity of Fishing Gears in a Multi-Species Indonesian Coral Reef Fishery

There are millions of small-scale fishers worldwide that rely on coral reefs for their livelihood. Yields from many of these coral reef fisheries, however, have been declining. In Indonesia and other coral reefs worldwide, management approaches are dominated by marine protected areas but other options including gear-restrictions may be feasible and more adaptive to local ecological and social conditions. Yet, there is little data on the impacts and selectivity of fishing gears for coral reef fisheries. In this paper, we present results from a case study on the island of Lombok, where we examine the selectivity and overlap in catch composition of the two main fishing gear types: spearguns and handlines. The catch per unit effort (CPUE) was greater in handlines than spearguns, 10.8 and 9.97 kg trip-1, respectively. The two gears targeted different fish communities with little overlap in dominant species, suggesting a partitioning of resources; handlines targeted piscivores, whereas spearguns targeted mostly herbivores. Mean trophic level was 3.6 for the handline catch and 2.8 for spearguns, where it was inversely related to CPUE. Spearguns captured more species overall and the number of species increased as the CPUE increased. Length parameters of maturity indicated that neither gear showed signs of (growth) overfishing and fishing grounds dominated by speargun fishers had catches associated with younger ages at first maturity than handlines. Our findings provide local baseline data on the potential utility of gear restrictions as a management tool. Specifically, managers could monitor reefs and reduce handlines when piscivorous fishes are low and on spearguns when species diversity is low or algal abundance is high. Should it become more desirable to implement ecosystem approaches to management that are adaptive to changing ecological and social conditions, these indicators may be used as starting points along with local management preferences of fishers