It is commonly assumed in surveys that the likelihood of capturing or observing individuals of a given species is constant. Yet evidence is building that catchability, or the likelihood of catching ...an individual present at a site, can vary.We used 5465 paired trap-video samples collected along the southeast US Atlantic coast in 2015−2018 to estimate trap catchabilities of 6 reef fish species (gray triggerfish Balistes capriscus, red porgy Pagrus pagrus, vermilion snapper Rhomboplites aurorubens, black sea bass Centropristis striata, red snapper Lutjanus campechanus, white grunt Haemulon plumierii) as the ratio of trap catch to standardized site abundance from corresponding videos. Species-specific trap catchabilities were then related to 2 primary predictor variables: water temperature and percent of the visible bottom consisting of rocky substrate. Water temperature strongly influenced trap catchabilities for all species after standardizing for all other variables. The 4 warm-water species displayed strong positive relationships between catchability and temperature; of these species, the smallest absolute increase in catchability occurred for vermilion snapper (0.0 at ~14°C to 0.05 at ~28°C) and the largest occurred for white grunt (0.0 at ~14°C to 0.49 at ~28°C). The 2 cooler-water species displayed either a dome-shaped (red porgy) or negative relationship (black sea bass) between catchability and temperature. Furthermore, trap catchabilities for all species declined substantially (42−80%) as the percent hard bottom of the site in - creased. Only when catchability is properly accounted for can results be considered unbiased and subsequent management advice be considered accurate.
The social structure of estuarine-resident bottlenose dolphins is complex and varied. Residing in habitats often utilized for resource exploitation, dolphins are at risk due to anthropogenic ...pressures while still federally protected. Effective conservation is predicated upon accurate abundance estimates. In North Carolina, two estuarine-resident stocks (demographically independent groups) of common bottlenose dolphin have been designated using spatiotemporal criteria. Both stocks are subjected to bycatch in fishing gear. The southern North Carolina estuarine stock was estimated at <200 individuals from surveys in 2006, which is outdated per US guidelines. Thus, we conducted a new capture-mark-recapture survey in 2018, identifying 547 distinct individuals, about three times higher than the prior abundance estimate. We compared those individuals to our long-term photo-identification catalog (1995–2018, n = 2,423 individuals), matching 228 individuals. Of those 228, 65 were also included in the 2013 abundance estimate for the northern North Carolina estuarine stock. Using sighting histories for all individuals in the long-term catalog, we conducted a social network analysis, which is independent of
a priori
stock assignments. The three primary clusters identified were inconsistent with current stock designations and not defined by spatiotemporal distribution. All three clusters had sighting histories in the estuary and on the coast, however, that with the highest within-cluster associations appeared to use estuarine waters more often. The within-cluster association strength was low for one cluster, possibly due to only part of that cluster inhabiting the southern North Carolina estuarine system. Between-cluster differences occurred in infestation rates by the pseudostalked barnacle,
Xenobalanus globicipitis
, but that did not predict clusters. We suggest the need to re-evaluate the stock structure of estuarine-resident common bottlenose dolphins in North Carolina and currently have insufficient information to assign an abundance estimate to a currently designated stock.
Extreme weather events strongly influence marine, freshwater, and estuarine ecosystems in myriad ways. We quantified movements of a demersal oceanic fish species (gray triggerfish Balistes capriscus; ...N = 30) before, during, and after two hurricanes in 2017 using fine-scale acoustic telemetry at a 37-m deep study site in North Carolina, USA. During storms, gray triggerfish movement and emigration rates were 100% and 2550% higher, respectively, than on days with no storms. We found that increased movement rates were much more strongly correlated with wave orbital velocity (i.e., wave-generated oscillatory flow at the seabed) than either barometric pressure or bottom water temperature, two covariates that have been demonstrated to be important for organisms in shallower water. Higher movement rates during storms were due to increased mobility at night, and emigrations typically occurred at night in the direction of deeper water. Overall, we found significant storm effects on the movement behavior of a demersal fish species in the open ocean, despite our study occurring in deeper water than previous studies that have examined storm effects on animal movement. We conclude that tropical storms are a driving force behind the structure of marine ecosystems, in part by influencing movements of mobile animals.
Most demersal fishes are difficult to observe and track due to methodological and analytical constraints. We used an acoustic positioning system to elucidate the horizontal and vertical movements of ...44 red snapper (Lutjanus campechanus) off North Carolina, USA, in 2019. Mean movement rate and distance off bottom varied by individual, with larger red snapper generally moving faster and spending more time farther off the bottom than smaller individuals. We used generalized additive mixed models that accounted for temporal autocorrelation in the data to show that mean hourly red snapper movement rate was lower during the day than at night and was negatively related to bottom water temperature. Moreover, red snapper spent more time off the bottom during the day than at night, and vertical movements were mostly related to bottom upwelling events that sporadically occurred in May-July. Our results and previous observations suggest that red snapper feed primarily on benthic organisms at night, and display diel vertical migration (i.e., thermotaxis) up to warmer waters (when present) during the day to aid digestive efficiency. Movement is a central organizing feature in ecology, and the sustainable management of fish will benefit from a better understanding of the timing and causes of fish movement.
Approaches towards habitat conservation and restoration often include supplementing or enhancing existing, degraded, or lost natural habitats. In aquatic environments, a popular approach towards ...habitat enhancement is the introduction of underwater human-made structures or artificial reefs. Despite the nearly global prevalence of artificial reefs deployed to enhance habitat, it remains debated whether these structures function similarly to comparable natural reefs. To help resolve this question, we conducted a literature review and accompanying meta-analysis of fish community metrics on artificial reefs within the coastal ocean and made comparisons with naturally-occurring reference reefs (rocky reefs and coral reefs). Our findings from a synthesis of 39 relevant studies revealed that, across reef ecosystems, artificial reefs support comparable levels of fish density, biomass, species richness, and diversity to natural reefs. Additional analyses demonstrated that nuances in these patterns were associated with the geographic setting (ocean basin, latitude zone) and artificial reef material. These findings suggest that, while artificial reefs can mimic natural reefs in terms of the fish assemblages they support, artificial reefs are not one-size-fits-all tools for habitat enhancement. Instead, artificial reefs should be considered strategically based on location-specific scientific assessments and resource needs to maximize benefits of habitat enhancement.
In modern fishery stock assessments, the productivity of exploited stocks is frequently summarized by a scale-invariant "steepness" parameter. This parameter, which describes the slope of the ...spawner-recruit curve, determines resilience of a stock to exploitation and is highly influential when estimating maximum sustainable yield. In this study, we examined conditions under which steepness can be estimated reliably. We applied a statistical catch-age model to data that were simulated over a broad range of stock characteristics and exploitation patterns and found that steepness is often estimated at its upper bound regardless of underlying productivity. The ability to estimate steepness reliably was most dependent on the true value of steepness, the exploitation history of the stock, natural mortality, duration of the time series, and quality of an index of abundance;; this ability was relatively unaffected by levels of stochasticity in recruitment and sampling intensity of age compositions. We further explored the method of inverse prediction to improve estimates of steepness and conclude that this approach holds promise. We illustrate the utility of simulation and inverse prediction methods with two fish stocks located off the southeastern United States, greater amberjack (
Seriola dumerili
) and gag grouper (
Mycteroperca microlepsis
).
We review three broad categories of risk assessment methodology used for cartilaginous fish: productivity-susceptibility analysis (PSA), demographic methods, and quantitative stock assessments. PSA ...is generally a semi-quantitative approach useful as an exploratory or triage tool that can be used to prioritize research, group species with similar vulnerability or risk, and provide qualitative management advice. Demographic methods are typically used in the conservation arena and provide quantitative population metrics that are used to quantify extinction risk and identify vulnerable life stages. Stock assessments provide quantitative estimates of population status and the associated risk of exceeding biological reference points, such as maximum sustainable yield. We then describe six types of uncertainty (process, observation, model, estimation, implementation, and institutional) that affect the risk assessment process, identify which of the three risk assessment methods can accommodate each type of uncertainty, and provide examples mostly for sharks drawn from our experience in the United States. We also review the spectrum of stock assessment methods used mainly for sharks in the United States, and present a case study where multiple methods were applied to the same species (dusky shark, Carcharinus obscurus) to illustrate differing degrees of model complexity and type of uncertainty considered. Finally, we address the common and problematic case of data-poor bycatch species. Our main recommendation for future work is to use Management Strategy Evaluation or similar simulation approaches to explore the effect of different sources of uncertainty, identify the most critical data to satisfy predetermined management objectives, and develop harvest control rules for cartilaginous fish. We also propose to assess the performance of data-poor and -rich methods through stepwise model construction.
Most reef fish surveys use bait to attract individuals to bite hooks, enter traps, or be counted on underwater video. The behavior of fish around baited gears, however, is poorly understood despite ...its importance for estimating catchability. We used a fine-scale acoustic positioning system to elucidate the movement behaviors of 11 telemetered gray triggerfish Balistes capriscus around 54 baited fish traps deployed at a 37 m deep site in Raleigh Bay, North Carolina, USA. Median positional error rates from a reference transmitter were 1–2 m, suggesting fish positions were accurate and precise. Overall, 104 170 spatial positions were determined for gray triggerfish over the 42 d study. There were 27 instances of telemetered gray triggerfish responding to baited fish traps. These fish responded from initial distances up to 312 m (mean = 68 m) from traps and spent 4–95% (mean = 35%) of their time within 20 m of traps. Using generalized additive models, we determined that telemetered gray triggerfish were most likely to respond to baited traps when they were initially located close to (<100 m), and down-current from, baited traps. There were substantial differences in gray triggerfish responses and water clarity across the 3 recapture periods, suggesting gray triggerfish use vision, olfaction, and perhaps sound to locate bait. Our modeling approach is general, and could be used to quantify the behavior of myriad organisms around sampling gears in various types of aquatic systems.
The behavior of fish around bait is poorly understood despite it being important for the fish catching process and estimating relative abundance. We used a fine-scale acoustic positioning system to ...quantify the movements of 26 red snapper (Lutjanus campechanus) around 120 bait deployments in 2019 at a natural reef site (∼37-m deep) in North Carolina, USA. There were 39 instances of tagged red snapper approaching bait during four baiting days, some of which approached due to apparent sensory cues (28%), while most approached incidentally (72%). Tagged red snapper approached bait from initial distances of 1 to 1147 m (median = 27 m; mean = 86 m), and took 0–77 min (mean = 22 min) to approach. Fish were more likely to approach bait if they were located close to, and down-current of, the bait at deployment. Our estimated effective fishing area of 2290 m
2
(within which >50% of red snapper responded to bait) could be used along with video counts and other information to estimate densities of red snapper.
Management strategy evaluation (MSE) has become a more common tool for engaging stakeholders in fisheries management, and stakeholder participation in MSE is increasingly recognized as a vital ...component of the process. The participation of stakeholders, specifically fishers, in MSE is of particular importance because they often possess intimate knowledge of the socio-ecological management system that MSE seeks to model. When the resources to conduct a “full” MSE with direct fisher involvement are unavailable, MSEs are sometimes conducted by desk-based analysts with no fisher engagement. We propose an intermediate framework in which information collected from semi-structured interviews is used to inform a “desk-based” MSE. We demonstrate that semi-structured interviews with commercial and recreational fishers can elicit some of the same kinds of information that fishers provide during direct participation in MSE. We conducted 30 semi-structured interviews with commercial and recreational fishers from the Southeast United States participating in either Atlantic cobia (
Rachycentron canadum
) or black sea bass (
Centropristis striata
) fisheries. We collected primarily qualitative and some quantitative information about preferred conceptual objectives and management measures, and how their fishing behavior has changed in response to past management action. Commercial fishers generally preferred conceptual objectives and management measures that align with traditional MSY-based fisheries management, while recreational fishers’ responses were substantially more heterogeneous, indicating a more diverse range of desired objectives and preferred management measures. We synthesized this information to develop a suite of management procedures that employ a range of fishing mortality-based constant-catch harvest control rules and size-based management measures for simulation testing against preferred objectives by sector. We demonstrate that integrating information from semi-structured interviews with MSE in this way offers a cost-effective alternative intermediate approach to fisher participation in MSE when direct participation is not possible.
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