Bycatch Mortality Research Articles

A Rapid Assessment of the Marine Megafauna Biodiversity Around South Bali, Indonesia

A low-cost, small-boat, rapid assessment survey was conducted on the waters off the southern Peninsula of Bali. The objectives were: (1) to conduct an inventory of cetacean species in the study area; (2) to map cetacean distribution to inform the design of the Badung MPA; (3) to estimate relative abundance of cetaceans and record information on presence and distribution of other marine megafauna; and (4) to train observers in the use of distance sampling methods. The survey adopted a “training while doing” approach to build local capacity for marine biodiversity monitoring, while collecting a snapshot of data to assess species richness and distribution. The survey accomplished its first two objectives, but due to violation of underlying assumptions, had mixed success with the third objective. Our survey revealed that the waters off the southern Peninsula of Bali support a rich cetacean fauna, with at least seven cetacean species, other marine megafauna, and avian species. Seven cetacean species found on our survey include: spinner dolphin (Stenella longirostris), pantropical spotted dolphin (Stenella attenuata), Fraser’s dolphin (Lagenodephis hosei), Risso’s dolphin (Grampus griseus), bottlenose dolphin (Tursiopssp.), Bryde’s whale (Balaenoptera edeni), and sperm whale (Physeter macrocephalus). Density estimates were low for all whales combined, but seem implausibly high for dolphins; likely due to violation of assumptions of distance sampling methods. Future surveys should include sufficient time for training to generate reliable abundance estimates. A dedicated bycatch study is needed to understand sustainability of bycatch mortality relative to reliable abundance estimates.

Mitigating the impact of longline fisheries on seabirds: Lessons learned from the South Georgia Patagonian toothfish fishery (CCAMLR Subarea 48.3)

Seabird mortality in fisheries is a global problem and a major driver of the continued decline of many seabird populations. Unless appropriate mitigation is in place, longline fishing can cause high levels of seabird mortality. Here we describe the development and implementation of seabird mitigation measures in the Patagonian toothfish Dissostichus eleginoides fishery around the sub-Antarctic islands of South Georgia (CCAMLR Subarea 48.3), since the fishery began in the late 1980s. The initial high bycatch mortality (>5000 birds / 0.59 birds per 1000 hooks in 1996) has been reduced to negligible levels (<0.01 per 1000 hooks) through implementation of a suite of mitigation measures and a high level of compliance. The principal species killed in the fishery were black-browed albatross and white-chinned petrels, with most of the mortality occurring in April and early May. Whilst the synchronous introduction of much of the mitigation makes it is difficult to confirm which measures have been most effective, there is compelling evidence that the restriction of the fishery to the austral winter was a major factor. Night-setting and line-weighting measures have also been important in reducing mortality and the 100% observer coverage in the fishery has encouraged high levels of compliance. We also consider how different measures may be effective for different species and how novel measures, such as the use of marked hooks, have helped encourage compliance. The mitigation measures developed in the South Georgia fishery have subsequently been adopted in other CCAMLR fisheries and have helped guide global best practice in addressing seabird bycatch.

Disentangling Natural and Anthropogenic Forms of Mortality and Serious Injury in a Poorly Studied Pelagic Dolphin

Killer whale (Orcinus orca) populations specialize in both prey and prey acquisition tactics around the world and may be a primary evolutionary driver of the habits of small cetaceans. Entanglement in fishing gear is the most significant anthropogenic threat to the survival of cetaceans worldwide. Distinguishing between natural and human-caused sources of mortality and injury is a key task in marine mammal conservation and management. In British Columbia (BC), Canada, mammal-eating killer whales co-occur with Pacific white-sided dolphins (Lagenorhynchus obliquidens). Bycatch mortality rates are unknown here due to lack of systematic fisheries observer coverage. Drawing from more than three decades of first-hand observations of killer whale attacks on Pacific white-sided dolphins, we identify common themes with respect to predatory behavior of killer whales and anti-predatory responses of dolphins. With input from veterinary pathologists, we outline clues to distinguish killer whale rake marks from scars and wounds likely to be caused by fishery interactions. We examined photographs of 415 well-marked Pacific white-side dolphins for evidence of injuries and scars consistent with either killer whale attacks or fishery interactions. In this case study, healed scars from interactions with killer whale predators were ∼8× more common than scars from fishery interactions (3.9 vs. 0.5%), suggesting that predation is a much bigger threat to Pacific white-sided dolphins in the study area than anthropogenic impacts, or that dolphins are much less likely to survive a fishery interaction than a predation attempt. To advance our knowledge on poorly studied species, multiple lines of evidence will be needed.

Raised‐Footrope Gill‐Net Modification Significantly Reduces Subadult Atlantic Sturgeon Bycatch

AbstractBycatch is a major problem in most commercial fisheries around the world and is among the greatest challenges for fisheries managers tasked with conserving, protecting, and sustaining marine resources. Bycatch of protected species is particularly problematic because even small levels of bycatch mortality can hinder conservation efforts. The federally protected Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus is one such example. Unknown numbers of Atlantic Sturgeon are caught as bycatch in commercial gill‐net fisheries along the U.S. Atlantic coast, with discard mortality rates as high as 51%. The Striped Bass Morone saxatilis sink gill‐net fishery in the James River, a tributary to Chesapeake Bay, is the only inshore fishery in Virginia with mesh sizes (13.3–20.3‐cm stretched mesh) that are large enough to have high levels of Atlantic Sturgeon bycatch. This study was conducted during the spring fishery and examined a modified gill‐net design that incorporated a raised footrope at the bottom of the net, creating an approximately 1‐m space between the benthos and the net. The modified net was fished alongside conventional commercial gear to evaluate catch rates of Striped Bass and Atlantic Sturgeon in each gear. Our findings showed that the experimental net significantly reduced bycatch of Atlantic Sturgeon (64.3%) and significantly increased the landings of Striped Bass (45.6%). This gear should be considered as a management option for the spring Striped Bass fishery in Virginia and any fishery in which subadult Atlantic Sturgeon are the primary bycatch. Additional research on seasonal orientation of Atlantic Sturgeon in the water column is needed before adopting the raised‐footrope design in the presence of adults on spawning runs.

Dynamics and Viability of a Small, Estuarine-Resident Population of Lahille’s Bottlenose Dolphins From Southern Brazil

Identifying threatened populations and quantifying their vulnerability is crucial for establishing priorities for conservation and providing robust information for decision-making. Lahille’s bottlenose dolphins have been long subjected to by-catch mortality in gillnet fisheries in coastal waters of southern Brazil, particularly in the Patos Lagoon estuary (PLE) and adjacent coastal waters, where dolphins from three populations (or Management Units) show overlapping home ranges. In this study we used a stage-classified matrix population model to conduct a demographic analysis of the PLE’s population with life-history data estimated through an 8 years mark-recapture study. A population viability analysis (PVA) was used to run a series of simulations where the risk was assessed under different by-catch scenarios, taking into account the effects of parameter uncertainty and stochasticity in the projections. In the absence of by-catch, we estimated that this dolphin population would growth at a rate of about 3% annually (95% CI: 1.2–5.8%). Under current by-catch rates, prognoses indicated high probabilities of viability over the next 60 years. These optimistic prognoses appear to be associated with the high survival of adult females. However, the eventual removal of very few mature females (one every year or two) would result in a prominent likelihood of decline from its current abundance at all pre-specified levels. The viability of the population would be substantially improved if the survival of juveniles/sub-adults could be increased. This may be achieved through the recently implemented dolphin protection area, which prohibits gillnet fisheries in the core area of this population. If the protection area reduces the entanglement rates of the most impacted life-stages (i.e., juvenile/sub-adult dolphins), there would be a substantial chance of the PLE’s dolphin population increasing above 20% of its current size, which is here proposed as conservation goal. If met, this goal has the potential to promote habitat quality, increase genetic diversity and connectivity with adjacent populations, enhancing the ability of bottlenose dolphins in southern Brazil to cope with environmental change and potential disease outbreaks.

Can we manage marine mammal bycatch effectively in low‐data environments?

Abstract Determining acceptable rates of human‐caused mortality in low‐data situations is a concern for many taxa world‐wide. An established approach for determining acceptable levels of human‐caused mortality of marine mammals and other species of conservation concern is the Potential Biological Removal (PBR) framework, but PBR requires near‐unbiased estimates of absolute abundance, constraining its use in systems with limited data. We develop three alternative methods for identifying acceptable levels of human‐caused mortality for long‐lived, slowly reproducing species, using indices of relative abundance combined with estimates of bycatch mortality in fisheries, and evaluate these methods using simulations similar to those used to develop PBR. Across a variety of scenarios, the parameters of the three methods can be tuned to achieve conservation performance similar to that of PBR in scenarios that represent nearly ideal conditions. However, these methods produce lower and more variable bycatch mortality limits, depend upon reasonably accurate estimates of bycatch mortality and are more sensitive to uncertainties. Synthesis and applications. Here we develop three alternative methods that expand the toolbox of approaches available for use in determining marine mammal conservation reference points for human‐caused mortality when it is not possible to apply the more standard, data‐hungry PBR approach. These approaches may be useful in supporting the establishment of new bycatch management programmes, or until estimates of absolute abundance become available.

Spatiotemporal models highlight influence of oceanographic conditions on common dolphin bycatch risk in the Bay of Biscay

The population of short-beaked common dolphins Delphinus delphis of the Bay of Biscay (northeast Atlantic) has been subjected to potentially dangerous levels of bycatch since the 1990s. As the phenomenon intensifies, it represents a potent threat to the population. Here, we investigated the relationship between bycatch mortality and oceanographic processes. We assumed that oceanographic processes spatiotemporally structure the availability and aggregation of prey, creating areas prone to attract both common dolphins and fish targeted by fisheries. We used 2 datasets from 2012 to 2019: oceanographic data resulting from a circulation model and mortality data inferred from strandings. The latter allows location of mortality areas and quantification of the intensity of mortality events at sea. We fitted a series of spatiotemporal hierarchical Bayesian models using integrated nested Laplace approximations (INLA). Results provided first insights on how bycatch of common dolphins in the Bay of Biscay might be related to key seasonal and dynamic oceanographic features. We showed that from a statistical predictive point of view, the monthly trend of 2019 bycatch mortality could be predicted with few oceanographic covariates. This study highlights how gaining knowledge about environmental influences on interactions between short-beaked common dolphins and fisheries could have great conservation and management value. Identified relationships with oceanographic covariates were complex, as expected given the dynamic aspects of oceanographic processes, dolphins and fisheries distributions. Further research focusing on smaller time scales is needed to elucidate proximal drivers of common dolphin bycatch in the Bay of Biscay.

Spatial assessment of albatrosses, commercial fisheries, and bycatch incidents on Canada’s Pacific coast

Fisheries bycatch mortality poses a primary threat to the majority of the world’s 22 albatross species, 15 of which are at risk of extinction. Although quantitative estimates of albatross bycatch are often unavailable due to a relative or total absence of monitoring, spatial overlap between fisheries and albatrosses is often used to estimate the extent of interaction, a proxy for exposure to bycatch, and to inform avoidance and mitigation actions. Using comprehensive records of commercial demersal longline and trap fishing and survey information for albatrosses (black-footed albatross Phoebastria nigripes, Laysan albatross P. immutabilis, short-tailed albatross P. albatrus), the extent of spatial potential interaction was estimated in Canada’s Pacific coast waters and examined across breeding and non-breeding seasons. The distributions of albatrosses and longline and trap fisheries were found to substantially overlap, with potential interaction hotspots concentrated along the continental shelf break. Trap fisheries reported 1 albatross bycatch incident, suggesting that these fisheries are responsible for negligible albatross mortalities. In contrast, &gt;80% of recorded albatross bycatch incidents occurred within 10 km of albatross-longline fisheries hotspot locations, providing evidence that longline-albatross potential interaction hotspots represent actual areas of elevated bycatch mortality risk. Indicative of potential conservation concern, 60% of short-tailed albatross sightings occurred within 10 km, and 93% within 30 km, of longline-albatross potential interaction hotspots. By contributing knowledge regarding albatross-fisheries interactions, in addition to undertaking the first evaluation of albatross-fisheries hotspots with recorded bycatch incidents on Canada’s Pacific coast, this study represents a step towards enhancing albatross conservation through bycatch avoidance and mitigation.

Assessing pinniped bycatch mortality with uncertainty in abundance and post-release mortality: A case study from Chile

The effects of human-caused mortality, such as fisheries bycatch, of endangered, threatened and protected (ETP) species of marine mammals can be evaluated using population model-based stock assessments. The information available to conduct such assessments is often very limited. Available data might include fragmented time-series of abundance estimates, incomplete data on bycatch for the fisheries that interact with ETP species (often few years and low observer coverage), and perhaps some data on scale and trends in fishing effort. Such data are challenging to use as the basis for stock assessments, which generally assume that estimates of removals (bycatch, in our context) through time are available for at least the most recent decade or two. This paper describes a stock assessment method for use with sparse observer data on bycatch mortality, applied within the context of a Bayesian estimation framework. The method produces estimates, with associated measures of precision, of population size and historical time-series of bycatch mortality that are consistent with the observer and abundance data. It provides a rigorous way to account for the uncertainty arising from animals that are caught but released alive and then die subsequent to release, given a post-release mortality rate prior. Observer data from industrial and artisanal purse seine and trawl fisheries and survey data for South American sea lions (Otaria byronia) and South American fur seals (Arctocephalus australis) off Chile are used to illustrate the method.

Spatial Distribution Changes and Habitat Use in Red Porgy in Waters off the Southeast U.S. Atlantic Coast

AbstractDespite 30 years of relatively strict management measures, the Red Porgy Pagrus pagrus population off the southeast U.S. Atlantic coast has not met rebuilding goals and was still categorized as overfished over a decade after a moratorium (SEDAR 2020). The lack of recovery indicates that limiting fishing pressure is not enough to effectively manage population levels. Population size may be driven by spatial or habitat associations independent of fishing pressure. We defined spatial distribution and habitat associations of Red Porgy adults and recruits by using a 23‐year, fishery‐independent trap catch time series (1996–2019). Abundance of recruits was below the long‐term average, and adults were declining for the last 8 years of the time series. In addition, the spatial distribution of recruits tended to contract to deeper waters in the center of the region when abundance was low, whereas adults remained relatively consistent in their spatial and depth distribution regardless of abundance. The independence between effective area occupied and adult abundance supports that adults persisted throughout the region, whereas recruit area occupied was proportional to abundance. Recruits and adults overlapped spatially, but there was some partitioning of habitats: recruits were more abundant in less‐complex habitats (low benthic biota coverage and low availability of hard substrate) relative to more complex habitats, and adults were more abundant in more complex or warm habitats than in less‐complex or cooler habitats. When overall abundance was reduced, adult abundance in more complex habitats became more similar to abundance in less‐complex habitats, while there was little to no change in recruit habitat use. The center of the region had a high overlap of adults and recruits, particularly in times of reduced recruitment. If fishers cannot target adults only, there is high potential for bycatch mortality or reduced fitness for recruits, which would further reduce the likelihood of recovery.

Mitigating Seafood Waste Through a Bycatch Donation Program

Discarding of prohibited, under-sized, or nontarget finfish is a major problem globally. Many such unwanted or banned catches do not survive long enough to be released alive, creating complex ecological and policy issues for the fishing industry. In U.S. Federal waters, regulation requires bycatch to be avoided as practicable and bycatch of some finfish species is designated as prohibited species catch (PSC). By regulation, PSC cannot be retained or sold and it must be returned to the sea (dead or alive). Some PSC species have strict limits to further incentivize their avoidance and limit bycatch mortality and these limits can lead to fishery closures. Despite extensive efforts to avoid bycatch in the U.S. and elsewhere, unwanted catches still occur, creating the potential for substantial food waste. We present one rarely discussed approach to maximize the value of dead, unwanted or prohibited finfish catches. The Prohibited Species Donation (PSD) program utilizes trawl fishery PSC that would otherwise be discarded by instead donating it to hunger relief organizations. This program simultaneously provides food and reduces waste while avoiding inadvertent incentives for catching prohibited species. For 26 years, the non-profit organization, SeaShare, has worked with the Alaska seafood industry to distribute 2660 t (~23.5 million servings) of prohibited species donations (salmon and halibut), high quality seafood that would have otherwise been discarded due to prohibition on retention. The PSD program provides an example that addresses food security and social value, an under-represented perspective in the global dialogue on unwanted catches.

Low spatial overlap between foraging shearwaters during the breeding season and industrial fisheries off the west coast of Portugal

Fisheries have impacted seabird populations worldwide, either via bycatch mortality or resource depletion. Understanding the overlap between seabird distributions and fisheries is an important element for bycatch risk assessment, though the drivers of variation in seabird-fishery overlap are not well understood for some seabird populations. Here, we quantified the spatial overlap between foraging Cory’s shearwaters Calonectris borealis during the breeding season and commercial fisheries operating within the Portuguese Exclusive Economic Zone. In addition, we evaluated whether overlap varied as a function of an individual’s boldness, sex or breeding stage. For this, we GPS tracked 361 foraging trips by 72 Cory's shearwaters nesting at Berlenga Island, Portugal, over 5 consecutive breeding seasons (2012-2016). Simultaneously, we used fishing effort data from Global Fishing Watch detailing the distribution of industrial fisheries within the temporal and spatial range of Cory's shearwater tracks. Although fishing vessels were present during 88.1% of foraging trips, Cory's shearwaters spent only on average 13.3% of the time foraging in the same areas as fisheries. Such low spatial overlap is likely driven by high prey availability near the colony and suggests low direct competition for resources. We also found variation in overlap with fisheries across the breeding period, with Cory's shearwaters spending approximately 11% more time foraging in the same areas as fixed gear and purse seine vessels during pre-laying than during chick-rearing. Surprisingly, no sex or boldness-related differences were found in the overlap with any fishing gear. Our findings have implications for understanding within population variation in the overlap between fisheries and seabirds and, in turn, bycatch risk.

Bowfishing in the United States: History, Status, Ecological Impact, and a Need for Management

In this paper we review the history and development of bowfishing, provide a case study of a high-profile bowfishing tournament in Oklahoma, survey and summarize management of the sport in all 50 states, and provide scientifically-based approaches for its management. Bowfishing has a distinct niche in the evolution of the bow and arrow and in fishing, as one of several methods practiced by many and scattered indigenous cultures worldwide. In the past century, advances in technology, including the development of the compound bow, custom boat and lighting systems for night bowfishing, and improved information transfer have opened the sport to many people previously unable to participate in the sport at a satisfying level. Bowfishing poses some distinct challenges for fisheries managers compared to angling, including the impracticality of catch-and-release, non-catch (wounding) mortality, and by-catch mortality of non-targeted native species. In 2019, we conducted a survey of 50 state fish and wildlife agencies that indicated only nine states had bowfishing education programs and none had articulated management goals or plans specific to the sport. Evidence indicates that bowfishing may provide plentiful opportunities for harvesting nuisance invasive species such as Asian carps (Cyprinidae) and the Common Carp Cyprinus carpio, but must be practiced much more judiciously, and in some instances, not at all, depending on locality, for higher valued native species such as buffalofishes (Catostomidae: Ictiobus spp.), Paddlefish Polyodon spathula, gars (Lepisosteidae), and rays (Batoidea). Whereas in the terrestrial and avian species that bowhunters most commonly target, males reach a larger size than females, in fish species targeted by bowfishers, the opposite is the case. The result is selective depletion of large, older, mature females and evolutionarily disruptive truncation of life histories. We suggest ten of many potential topics for consideration in agency management planning for bowfisheries. We seek to provide agencies information for developing historical, ecological, and socioeconomic perspectives for managing bowfisheries, as other fisheries, as instruments of species conservation, public benefit, and sound long-term public policy.

Modified Commercial Fish Trap to Help Eliminate Salmonid Bycatch Mortality

AbstractThe utility of commercial salmonid Oncorhynchus spp. traps in the U.S. Pacific Northwest was recently revisited for the first time in decades to enable selective harvesting of hatchery‐origin salmonids while reducing mortality of Endangered Species Act (ESA)‐listed salmonids. Modifications to historical gear designs resulted in dramatic improvements in salmonid bycatch survival rates relative to conventional commercial gears in the lower Columbia River. Expanding upon this work, an experimental commercial fish trap was further modified to largely eliminate net contact, air exposure, handling, and crowding of fish. Studies were conducted from May to November 2019 in the lower Columbia River to estimate survival of bycatch and evaluate potential benefits from the modified passive capture design. Analyzed through two separate survival estimation techniques, the modified trap demonstrated no detectable effect on salmon release survival and a significant improvement over the previous prototype design. Estimated through a paired release–recapture methodology, the relative survival effect of catch and release compared to controls over a 400‐km migration was 1.017 ( = 0.032) for adult Sockeye Salmon O. nerka. For adult Coho Salmon O. kisutch that were held captive for a 48‐h postrelease period, estimated survival (S) was 1.000 (lower 95% confidence limit: S ≥ 0.978). These results suggest that trap modifications can be made to significantly reduce bycatch mortality of ESA‐listed salmonids and provide increased opportunity for harvest of hatchery‐origin salmonids.

Freshwater turtle bycatch research supports science‐based fisheries management

AbstractAlthough it is sometimes difficult for researchers to ensure that their work is used by resource managers to make informed decisions, an example where this knowledge–action gap has been breached is in research published inAquatic Conservation: Marine and Freshwater Ecosystems(AQC) – among other journals – that has assisted fisheries managers in identifying strategies for reducing freshwater turtle bycatch in commercial hoop net fisheries in Ontario, Canada.Research published in AQC has provided evidence towards a simple and effective method for preventing turtle bycatch mortality in hoop nets, which could be adopted by the fishers. Other research published in AQC evaluated the effect of bycatch mortality on the probability of persistence of turtle populations with population viability analyses, and outlined the need to minimize bycatch mortality to prevent local extirpation. Nine other papers have been published on freshwater turtle bycatch in Ontario, furthering our knowledge on this issue including seasonality and temperature effects on catches, other net modifications, post‐release effects and assisted recovery, and the perspectives of fishers.The research results were presented to local resource managers with further discussions involving industry and stakeholders to minimize turtle bycatch mortality. Over several years, researchers have provided information to resource managers; however, when an incident of high turtle mortality caught the public eye, the research was readily available and changes in regulations were quick to occur.Reasonably good communication among researchers, resource managers, industry, stakeholders, and the broader public allowed the rapid implementation of regulations to mitigate freshwater turtle bycatch mortality and bridged the knowledge–action gap between researchers and resource managers.Both articles published in AQC had practical conservation impacts and were influential in providing local resource managers with feasible solutions, and the impetus to change regulations. These impacts extended to other jurisdictions and their monitoring programmes, where methods to reduce turtle bycatch mortality were also implemented.

The ups and downs of traps: environmental impacts, entanglement, mitigation, and the future of trap fishing for crustaceans and fish

Abstract Fishing has many types of impacts on the marine environment. Degradation of seafloor habitats by trawling has been widely studied, along with bycatch mortality, and ghost fishing by traps. Traps or pots are commonly used for catching crustaceans and other organisms, but little research has been conducted on the environmental impacts of trap fishing. Trap fishing causes direct impacts on benthic habitats during setting and retrieval, including dragging along the seafloor, which can lead to the damage and destruction of habitat components such as corals, sponges, and other epifauna. Lines connecting multiple traps increase the overall footprint and cause additional damage. Lost traps and debris can cause damage to coral, submerged aquatic vegetation, and epifauna, especially if moved by storms. Although the trap footprint is small, movement of the trap can expand the impact footprint by an order of magnitude. Trap lines cause whale entanglement and death, and there is much interest in reducing the number of vertical lines as well as their potential for entanglement. New technologies for deploying, locating, and recovering traps are now being developed. The future of trap fisheries will require research on new ways to reduce their negative impacts on benthic and pelagic resources.

Evaluating management strategies for marine mammal populations: an example for multiple species and multiple fishing sectors in Iceland

A management strategy evaluation (MSE) is used to estimate success at achieving conservation goals for marine mammals while also aiming to minimize impacts on commercial fisheries. It is intended to improve understanding of US import rules that require countries exporting fish and fish products to the USA to adhere to marine mammal bycatch standards “comparable” to those used by the USA. The MSE framework is applied, for illustrative purposes, to export fisheries in Iceland that impact harbor porpoises (Phocoena phocoena), harbor seals (Phoca vitulina), and grey seals (Halichoerus grypus). Several management strategies are evaluated. The harbor porpoise population is estimated to be close to or above its maximum net productivity level (MNPL) and, according to the model, will continue to increase even if current levels of human-caused mortality are unchanged. In contrast, the grey seal and harbor seal populations are below MNPL, and bycatch mortality in the lumpfish (Cyclopterus lumpus) fishery will need to be reduced to allow them to recover to MNPL.

Movements of loggerhead sea turtles (Caretta caretta) in the Gulf of California: integrating satellite telemetry and remotely sensed environmental variables

AbstractThe loggerhead turtle (Caretta caretta) is a circumglobal species and is listed as vulnerable globally. The North Pacific population nests in Japan and migrates to the Central North Pacific and Pacific coast of North America to feed. In the Mexican Pacific, records of loggerhead presence are largely restricted to the Gulf of Ulloa along the Baja California Peninsula, where very high fisheries by-catch mortality has been reported. Records of loggerhead turtles within the Sea of Cortez also known as the Gulf of California (GC) exist; however, their ecology in this region is poorly understood. We used satellite tracking and an environmental variable analysis (chlorophyll-a(Chl-a) and sea surface temperature (SST)) to determine movements and habitat use of five juvenile loggerhead turtles ranging in straight carapace length from 62.7–68.3 cm (mean: 66.7 ± 2.3 cm). Satellite tracking durations ranged from 73–293 days (mean: 149 ± 62.5 days), transmissions per turtle from 14–1006 (mean: 462 ± 379.5 transmissions) and total travel distance from 1237–5222 km (mean: 3118 ± 1490.7 km). We used travel rate analyses to identify five foraging areas in the GC, which occurred mainly in waters from 10–80 m deep, with mean Chl-aconcentrations ranging from 0.28–13.14 mg m−3and SST ranging from 27.8–34.4°C. This is the first study to describe loggerhead movements in the Gulf of California and our data suggest that loggerhead foraging movements are performed in areas with eutrophic levels of Chl-a.

Ineffectiveness of light emitting diodes as underwater deterrents for Long-tailed Ducks Clangula hyemalis

Gillnet bycatch accounts for over 400,000 bird mortalities worldwide every year, affecting a wide variety of species, especially those birds that dive when foraging. Technological solutions to improve gillnet visibility or deter birds from approaching nets, such as LED lights, are essential for aiding diving birds to perceive nets as a hazard. Designing such solutions requires obtaining visual and behavioural ecology information from species to assess their ability to see the warning devices, and to examine their behavioural responses to them. Seaducks, particularly Long-tailed Ducks Clangula hyemalis, have high bycatch mortality rates. We examined the visual fields of four Long-tailed Ducks to understand their three-dimensional view around the head. The visual field characteristics of this species indicate a reliance on visual guidance for foraging associated with their capture of varied, mobile prey in their generalist diet. We subsequently conducted dive tank trials to test the effectiveness of 12 different LED treatments as visual deterrents to the underwater foraging behaviour of 8 Long-tailed Ducks. During each trial, ducks were offered food rewards from a specific underwater location in a dive tank, having the choice of whether to take the food or not. At the same time, they were exposed to either one LED light or the control (no light) to determine whether the presence of each light affected the foraging success rate of dives compared to the control. Exposure of ducks to all 13 treatment combinations was randomised over the trial period. White lights with an increasing flash rate were shown to have a significant positive effect on foraging success, and likely acted as a visual attractant, rather than as a deterrent. No light treatment significantly reduced the foraging success of ducks. LED lights did not inhibit the feeding of Long-tailed Ducks. Such lights may be ineffective as underwater visual deterrents when deployed on gillnets, while white flashing lights may make foraging sites more attractive to Long-tailed Ducks.

Changes in Shrimping Effort in the Gulf of Mexico and the Impacts to Red Snapper.

Despite a complex management landscape and decades of overfishing, Red Snapper (Lutjanus campechanus) stocks have grown substantially in the Gulf of Mexico and restrictions on the fisheries that catch them are being loosened. This year, annual shrimping effort was allowed to increase by 21% after National Marine Fisheries Service scientists concluded that the resulting bycatch of Red Snapper would only reduce the annual allowable catch in other fisheries by ∼1% and have no impact on population growth. Nonetheless, the recreational fishing sector intensely campaigned against this rule, fueled by wild mischaracterization of shrimp trawl bycatch in media outlets targeting anglers. Here, we aim to elevate the debates surrounding Red Snapper management by presenting scientific and historical context for the potential impacts from shrimping. We discuss our views of the current problems facing Red Snapper and key ecological questions to address for more effective management of this resource.