We estimated survival rates of discarded black sea bass (Centropristis striata) in various release conditions using tag–recapture data. Fish were captured with traps and hook and line from waters ...29–34 m deep off coastal North Carolina, USA, marked with internal anchor tags, and observed for release condition. Fish tagged on the bottom using SCUBA served as a control group. Relative return rates for trap-caught fish released at the surface versus bottom provided an estimated survival rate of 0.87 (95% credible interval 0.67–1.18) for surface-released fish. Adjusted for results from the underwater tagging experiment, fish with evidence of external barotrauma had a median survival rate of 0.91 (0.69–1.26) compared with 0.36 (0.17–0.67) for fish with hook trauma and 0.16 (0.08–0.30) for floating or presumably dead fish. Applying these condition-specific estimates of survival to non-tagging fishery data, we estimated a discard survival rate of 0.81 (0.62–1.11) for 11 hook and line data sets from waters 20–35 m deep and 0.86 (0.67–1.17) for 10 trap data sets from waters 11–29 m deep. The tag-return approach using a control group with no fishery-associated trauma represents a method to accurately estimate absolute discard survival of physoclistous reef species.
Mercury in seafood is a neurotoxicant that threatens human health. Dynamic rates of mercury emission, re-emission, and atmospheric deposition warrant studies into mercury concentrations in fish ...because many are consumed by humans and can serve as sentinels of mercury levels in the environment. We modeled trends in total mercury content in an apex marine fish predator, Atlantic blue marlin Makaira nigricans, whose muscle tissues were opportunistically sampled from North Carolina (USA) sportfishing tournaments over a discontinuous time period: between 1975 and 77 and 1998–2021 (n = 148). The model-estimated influence of marlin weight on total mercury concentration was constant across years (shared slope) allowing for comparisons of weight-corrected mercury concentrations among years. Weight-corrected total mercury concentrations revealed an inter-decadal decline of approximately 45 % between the 1970s and late 1990s and then variable but relatively stable concentrations through 2021. The mean (SD) wet weight concentration of total mercury was 9.47 (4.11) from 1975 to 77 and 4.17 (2.61) from 2020 to 2021. Methylmercury and selenium were measured on a subset of fish to address questions related to human health and consumption. Methylmercury levels (mean = 0.72 μg/g) were much lower than total mercury (mean = 4.69 μg/g) indicating that total mercury is not a good proxy for methylmercury in Atlantic blue marlin. Selenium, examined as a Se:Hg molar ratio and as a selenium health benefit value (HBVSe), showed high protective value against mercury toxicity. Long-term trends in the concentration of mercury in blue marlin should continue to be monitored to determine whether policies to mitigate anthropogenic contributions to global mercury are achieving their intended goals and to provide information to inform safe human consumption.
Display omitted
•Long-term studies of offshore marine apex predators are valuable for indexing ambient heavy metal concentrations.•Atlantic blue marlin muscle collected from 1975 to 2021 was analyzed for total mercury, methylmercury, and selenium.•Total mercury concentrations declined from the 1970s to late 1990s, but remained approximately constant during this century.•Methylmercury is a small percentage of total mercury in Atlantic blue marlin, which is not typically observed in fish.•High selenium concentrations in Atlantic blue marlin tissue may substantially offset mercury toxicity in human consumers.
It is unclear how urbanization affects secondary biological production in estuaries in the southeastern USA. We estimated production of larval/juvenile Fundulus heteroclitus in salt marsh areas of ...North Carolina tidal creeks and tested for factors influencing production. F. heteroclitus were collected with a throw trap in salt marshes of 5 creeks subjected to a range of urbanization intensities. Multiple factor analysis (MFA) was used to reduce dimensionality of habitat and urbanization effects in the creeks and their watersheds. Production was then related to the first 2 dimensions of the MFA, month, and year. Lastly, we determined the relationship between creek-wide larval/juvenile production and abundance from spring and abundance of adults from autumn of the same year. Production in marsh (g m−2 d−1) varied between years and was negatively related to the MFA dimension that indexed salt marsh; higher rates of production were related to creeks with higher percentages of marsh. An asymptotic relationship was found between abundance of adults and creek-wide production of larvae/juveniles and an even stronger density-dependent relationship was found between abundance of adults and creek-wide larval/juvenile abundance. Results demonstrate (1) the ability of F. heteroclitus to maintain production within salt marsh in creeks with a lesser percentage of marsh as long as this habitat is not removed altogether and (2) a density-dependent link between age-0 production/abundance and subsequent adult recruitment. Given the relationship between production and marsh area, natural resource agencies should consider impacts of development on production when permitting construction in the southeastern USA.
We sampled variably altered tidal creeks to determine community structure in a developing coastal (USA) landscape. Throw trapping collected smaller and juvenile nekton in the vegetated marsh while ...minnow trapping in unvegetated channels targeted relatively larger fishes. Non-metric multidimensional scaling ordinations were used to assess community structure. Environmental factors and species most rank-correlated with community dissimilarities in ordinations were determined through the nonparametric BIOENV analysis. We found differences in community composition among creeks that were largely consistent in 2 years. Juveniles of the dominant salt marsh fish Fundulus heteroclitus from throw trapping had a pattern opposite of amphipods and associated with creeks with marsh downstream while larger F. heteroclitus (from minnow trapping) associated with creeks with high percentages of marsh coverage and lower watershed imperviousness. A transient fish Lagodon rhomboides was associated with creeks with lower marsh percentages. Results indicate that loss of marsh, and breaks in marsh connectivity to areas downstream of tidal creeks, can lead to reduced abundances of a dominant resident marsh fish. In order to maintain production of marsh fishes, planners should prioritize the maintenance of intact salt marsh habitats and natural landforms.
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.
We used fish body depth to predict trap center-to-center mesh sizes that would optimize size selection of black sea bass Centropristis striata for both current and proposed minimum size limits for ...this species. We fished trap types of five different square mesh sizes/configurations: (1) 38.1mm mesh, (2) 38.1mm mesh on five sides and 50.8mm mesh on one side (back panel trap), (3) 50.8mm mesh, (4) 57.2mm mesh, and (5) 63.5mm mesh. The 38.1mm mesh trap was the control trap type. Back panel traps are the minimally legal mesh configuration in this region while 50.8mm mesh traps are commonly used in this fishery to further reduce culling of sub-legal black sea bass by fishers. Two previously untested mesh sizes, 57.2 and 63.5mm, were evaluated because a previously published morphometric relationship between black sea bass body depth and total length (TL) predicted that the diagonal openings of these two respective mesh sizes would retain black sea bass close to the current (279mm) and proposed minimum TL limits (305mm). We estimated size selection of each experimental trap type by comparing catches of control and experimental traps. All but the back panel trap displayed relatively steep selection around the fish length at which 50% of individuals were selected (l50). Initial size at retention (l10) by the 57.2 and 63.5mm trap types were nearly identical to current and proposed minimum fish sizes, respectively. Predictions from the body depth: TL relationship were very similar to estimates of l10 and l50, based on uncompressed body depth and compression to 93%. The 57.2mm mesh and 63.5mm mesh trap types maintained catches of legal fish but reduced catches of sub-legal fish compared to the back panel and 50.8mm mesh trap types. Relative to back panel and 50.8mm mesh traps, use of 57.2mm mesh traps would reduce rates of discard and discard mortality given current size limits in this fishery.
Development in the southeastern US coastal plain generates the need for a better understanding of how survival and abundance of estuarine nekton respond to urbanization. Apparent survival and density ...of the dominant Atlantic coast salt marsh fish, the mummichog Fundulus heteroclitus, were estimated in four North Carolina tidal creeks using a model simultaneously fitted to mark-resight and mark-recapture data. Rates of weekly loss (mortality plus emigration) were high (~ 10 %). Sampling for tagged fish within and outside of study creeks showed high site fidelity to each creek, indicating that loss largely resulted from mortality rather than emigration. Estimated rates of apparent survival were lowest in the creek with the least instream-and watershed-level impacts. This creek has direct (non-culvert) access downstream to a larger waterbody, suggesting that enhanced access by predators and/or greater rates of permanent emigration may have contributed to lower apparent survival in this creek. There was a positive relation between minnow trap catch-per-unit-effort (CPUE) and density allowing the relationship between CPUE and habitat and urbanization to be examined in a total of six creeks. The largest CPUE estimates occurred early in each growing season and were associated with creeks possessing characteristics most representative of undisturbed salt marsh mosaics: high percentage of marsh coverage instream and downstream and high percentage of marsh edge. Given generally limited movement outside of creeks, differences in abundance among creeks likely result from different levels of recruitment that are related to salt marsh availability. Priority preservation of salt marsh habitats may be warranted by natural resource planners to maintain abundance levels of this trophically important species.
We evaluated the performance of small (12.5 mm long) passive integrated transponder (PIT) tags and custom detection antennas for obtaining fine-scale movement and demographic data of mummichog ...Fundulus heteroclitus in a salt marsh creek. Apparent survival and detection probability were estimated using a Cormack Jolly Seber (CJS) model fitted to detection data collected by an array of 3 vertical antennas from November 2010 to March 2011 and by a single horizontal antenna from April to August 2011. Movement of mummichogs was monitored during the period when the array of vertical antennas was used. Antenna performance was examined in situ using tags placed in wooden dowels (drones) and in live mummichogs. Of the 44 tagged fish, 42 were resighted over the 9 mo monitoring period. The in situ detection probabilities of the drone and live mummichogs were high (~80−100%) when the ambient water depth was less than ~0.8 m. Upstream and downstream movement of mummichogs was related to hourly water depth and direction of tidal current in a way that maximized time periods over which mummichogs utilized the intertidal vegetated marsh. Apparent survival was lower during periods of colder water temperatures in December 2010 and early January 2011 (median estimate of daily apparent survival = 0.979) than during other periods of the study (median estimate of daily apparent survival = 0.992). During late fall and winter, temperature had a positive effect on the CJS detection probability of a tagged mummichog, likely due to greater fish activity over warmer periods. During the spring and summer, this pattern reversed possibly due to mummichogs having reduced activity during the hottest periods. This study demonstrates the utility of PIT tags and continuously operating autonomous detection systems for tracking fish at fine temporal scales, and improving estimates of demographic parameters in salt marsh creeks that are difficult or impractical to sample with active fishing gear.
Estimates of animal abundance are widely used to support conservation and resource management. For populations in open systems, abundance estimates from tagging data can be highly uncertain or ...biased. Here, we develop a novel approach to estimate abundance of an open population by pairing two models, each utilizing distinct tagging data. Using data from telemetry tags, we infer movement rates to and from the study site with a Markovian model allowing for an environmental effect. Then, using data from conventional passive tags, we apply a Lincoln–Petersen abundance estimator modified to account for mortality and movement. After developing the model within a Bayesian framework, we demonstrate its application to data on gray triggerfish (Balistes capriscus) tagged in the Atlantic Ocean off North Carolina, USA. For this open population, we estimate site abundance to be ∼1000 fish (∼2000 fish·km
–2
) and additionally find evidence for an effect of hurricanes on movement. The general approach may be useful for fisheries, wildlife, and other ecological studies utilizing multiple tag types, particularly for estimating abundance of an open population.
