The specific biological impacts of anthropogenic activities and associated fragmentation of estuarine habitats remain understudied. We compared nekton communities and fish movement at 9 road ...crossings (with culverts) and a tenth crossing (‘reference’ crossing that lacked a road or a culvert) in first-order Spartina alterniflora-dominated tidal creeks in coastal North Carolina. Sample sites were located on both sides of each crossing. Percent salt marsh and increasing water depth were factors that most contributed to dissimilarities in biological communities among sample sites; the resident salt marsh fish Fundulus heteroclitus dominated the catch at sites with high percentages of marsh and inherently shallow depths while a transient species Lagodon rhomboides dominated at deeper sites where marsh was absent. F. heteroclitus was marked with injectable elastomer to determine factors influencing its movement probability to sites on sides of crossings opposite from where it was tagged. The probability of F. heteroclitus moving was positively related to the percentage of marsh-fringed shoreline within its published home range and was highest at intermediate water depths. The results show that preserving salt marsh adjacent to road crossings will maintain communities and movement rates reflective of non-impacted habitats in tidal creeks in the US South Atlantic coastal plain and emphasize habitat connectivity as an ecological factor important to community structure and movement.
Objective
Our objective was to use sportfishing tournament data to determine whether sizes of Dolphinfish Coryphaena hippurus have been changing in the western North Atlantic (WNA) over recent ...decades.
Methods
We sampled North Carolina, South Carolina, and Florida marine sportfishing tournament landings for Dolphinfish lengths. Linear models were separately fitted to length data for males and females by regressing length against year. A subset of these models (analysis of covariance) considered tournament as a factor.
Result
An analysis of covariance model with a separate regression slope for each tournament provided the best fit to the data for male and female Dolphinfish. Meaningful temporal declines in the length of males and females were found for four of the five tournaments (no changes in length were observed for the fifth tournament). Median total length declines of 168, 105, 103, and 426 mm were predicted for males, and declines of 354, 133, 131, and 246 mm were predicted for females. Declines in the largest observed sizes of Dolphinfish (97.5% confidence limit) were found for most tournament‐ and sex‐specific combinations of data and could suggest excess fishing mortality on the population.
Conclusion
Declines in Dolphinfish size in the WNA region could have ramifications for conservation of the population given that these size changes translate into reduced individual fecundity of female Dolphinfish. Causes of the size decline could be fishing effects, environmental effects, or a combination of these. Reductions in individual size may be occurring simultaneously with declines in abundance identified in other recent research using fishery‐dependent data collected in the WNA.
Impact statement
Using fishery‐dependent data to study changes in fish size can be difficult because the assumption of constant selectivity is infrequently met. Our study shows the utility of using sportfishing tournament data to track changes in fish size when selectivity can be assumed to remain constant throughout the sampling period. Our results are informative for U.S. federal fishery managers who are considering updates to output controls (e.g., size limits and bag limits) to help conserve the Dolphinfish stock in the western North Atlantic region.
Estimates of discard mortality are difficult to obtain. Meta-analysis or life-history-based approaches to estimate discard mortality could provide informed estimates when direct empirical estimates ...are not available. We used data from published literature across a variety of fish species to determine if hooking condition (good vs. poor) and species-specific values for the Brody growth coefficient (K: a measure of fish physiology) were meaningful factors influencing discard mortality in hook and line fisheries. We then examined whether a two-step approach, combining condition- and physiology-specific estimates of discard mortality with data on proportion-by-hooking-condition hooking information for a fishery, could result in an estimate of discard mortality for dolphinfish Coryphaena hippurus comparable to an empirical estimate. A model with hooking condition, K and their interaction best fitted the published discard mortality data. K was an important negative covariate of discard mortality for good hooking condition, with higher K species experiencing greater rates of survival. In contrast, species in poor condition had similarly low rates of survival across a range of K values. Results suggests that hooking condition is the dominant source of mortality when fish are hooked in vital areas but that physiology should also be taken into account when estimating discard mortality for good condition fish. For the recreational dolphinfish fishery in the southeastern US, we estimated a median proportional discard mortality rate of 0.12 (95 % credible set: 0.07, 0.17) when combining the meta-analysis and field-collected proportion-by-condition data. This estimate was lower than the empirical estimate of dolphinfish discard mortality but the credible sets overlapped (median: 0.25; 95 % credible set: 0.05, 0.39). Estimates of discard mortality from our meta-analytic approach may be applicable to fisheries where empirical estimates of discard mortality are not available and hooking injuries are the dominant source of mortality.
Gillnets fished in North Carolina, USA, estuaries have high rates of bycatch relative to the target catch of southern flounder, Paralichthys lethostigma Jordan & Gilbert. This study tested whether ...rectangular‐mesh gillnets would maintain catch rates of southern flounder and reduce fish bycatch relative to conventional diamond‐mesh gillnets in two North Carolina estuaries. In the Neuse River estuary, catch rates of legal southern flounder were not different between the two mesh shapes, but the bycatch of red drum, Sciaenops ocellatus (Linnaeus) and other fish species was reduced with rectangular‐mesh net. In the Newport River estuary, southern flounder and red drum catches were reduced in rectangular‐mesh net, but the decrease was greater for red drum. Catches of sublegal southern flounder were reduced in the rectangular‐mesh net in both estuaries. Reduced catch rates of sublegal southern flounder and bycatch species suggest rectangular mesh may help manage stocks of estuarine fish species in areas where gillnets are used to target flatfishes.
Reliable data on reef fishes inhabiting the southeastern United States (North Carolina to Florida) continental shelf large marine ecosystem are difficult to obtain; catch quotas and time and area ...closures limit the collection of fishery-dependent samples. Further, unbiased fishery-independent samples are expensive to collect with conventional fishing gear. Consequently, stock assessments are often data-limited, especially for deepwater reef species. We estimated the relative abundance of deepwater reef fish with a double sampling approach using fisheries acoustics and conventional fishing gear (hook and line and chevron traps). Double sampling occurred within the newly-created Snowy Wreck Marine Protected Area and a nearby control site. Reef fish concentrations were identified by a single-beam Simrad ES60 transceiver with a transducer operating at 38
kHz. Hook and line samples were collected at 73 acoustic events, and chevron trap samples were collected at 20 acoustic events. The relationship between fisheries acoustic data and catch-per-unit-effort (CPUE) data was examined to develop a model to predict species-generic CPUE at unfished locations. Akaike's Information Criteria (AIC) found equal support for linear, exponential, and power relationships between acoustic backscatter and CPUE for each conventional fishing gear. Further model development would be aided by refining acoustic target information and applying complimentary fish sampling gears (i.e., split-beam fisheries acoustics gear, underwater video). Given further development, a double sampling design should be useful to estimate the relative abundance of important deepwater reef species over a wide area of the shelf break off the southeastern United States, utilizing either survey vessels or vessels-of-opportunity to rapidly collect acoustic samples.
Diet, gastric evacuation rates, daily ration, and population-level prey demand of bluefin tuna (Thunnus thynnus) were estimated in the continental shelf waters off North Carolina. Bluefin tuna ...stomachs were collected from commercial fishermen during the late fall and winter months of 2003-04, 2004-05, and 2005-06. Diel patterns in mean gut fullness values were used to estimate gastric evacuation rates. Daily ration determined from mean gut fullness values and gastric evacuation rates was used, along with bluefin tuna population size and residency times, to estimate population-level consumption by bluefin tuna on Atlantic menhaden (Brevoortia tyrannus). Bluefin tuna diet (n=448) was dominated by Atlantic menhaden; other teleosts, portunid crabs, and squid were of mostly minor importance. The time required to empty the stomach after peak gut fullness was estimated to be 620 hours. Daily ration estimates were approximately 2% of body weight per day. At current western Atlantic population levels, bluefin tuna predation on Atlantic menhaden is minimal compared to predation by other known predators and the numbers taken in commercial harvest. Bluefin tuna appear to occupy coastal waters in North Carolina during winter to prey upon Atlantic menhaden. Thus, changes in the Atlantic menhaden stock status or distribution would alter the winter foraging locations of bluefin tuna.
Minimum size limits may be ineffective for reef fishes because they often sustain barotrauma when caught from deep (>20 m) waters. A study was undertaken in conjunction with hook-and-line commercial ...fishermen to calculate discard percentages and evaluate potential release mortality of eight economically important species: black sea bass, Centropristis striata (Linnaeus), red grouper, Epinephelus morio (Valenciennes), snowy grouper, Epinephelus niveatus (Valenciennes), gag, Mycteroperca microlepis (Goode and Bean), scamp, Mycteroperca phenax (Jordan and Swain), vermilion snapper, Rhomboplites aurorubens (Cuvier), white grunt, Haemulon plumieri (Lacepède) and red porgy, Pagrus pagrus (Linnaeus). Fishing with baited hook and line occurred in 2004 and 2005 in Onslow Bay, NC, in waters 19-150 m deep. Sub-legal discard rates were 15% for vermilion snapper, 25% for red porgy, 7% for red grouper, 33% for gag, 35% for scamp and 12% for black sea bass. Although mortality based on post-release behaviour was relatively low, higher mortalities estimated from models incorporating hooking location and depth of capture suggest that minimum size limits may not provide the population benefits intended by management in the North Carolina reef fishery.
We compared numbers of strikes, proportions of fish that hooked up after strikes, proportions of fish that stayed on hook (retained) after hook up, and numbers of fish caught between circle and J ...hooks rigged with dead natural fish bait (ballyhoo) and trolled for three oceanic predator species: dolphinfish (Coryphaena hippurus), yellowfin tuna (Thunnus albacares), and wahoo (Acanthocybium solandri). Interactions were compared between circle and J hooks fished on 75 trips by two user groups (charter and recreational fishermen). Hooks were affixed to three species-specific leader types most commonly fished in this region: monofilament (dolphinfish), fluorocarbon (tuna), and wire (wahoo). Numbers of fish caught per trip and three potential mechanisms that might influence numbers caught (i.e., number of strikes, proportion of fish hooked, and proportion retained) were modeled with generalized linear models that considered hook type, leader type, species, user (fishing) group, and wave height as main effects. Hook type was a main effect at the catch level; generally, more fish were caught on J hooks than on circle hooks. The effect of hook type on strike rates was equivocal. However, J hooks had a greater proportion of hook-ups than did circle hooks. Finally, the proportion of fish retained once hooked was generally equal between hook types. We found similar results when data from additional species were pooled as a "tuna" group and a "mackerel" group. We conclude that J hooks are more effective than circle hooks at the hook-up level and result in greater numbers of troll-caught dolphinfish, tunas, and mackerels.
We collected 1,399 striped bass Morone saxatilis from western Albemarle Sound, North Carolina, during May through October of 2002 and 2003 to characterize diet, prey type selectivity, and prey size ...selectivity. Herrings Alosa spp., Atlantic menhaden Brevoortia tyrannus, bay anchovy Anchoa mitchilli, silversides Menidia spp., and yellow perch Perca flavescens dominated the diets of age‐1 striped bass, while Atlantic menhaden dominated the diets of older striped bass. Selectivity was calculated for three categories of striped bass (ages 1, 2, and 3+ 3–7) based on fish prey collections from a 61‐m beach seine and a 76‐m purse seine. Striped bass of all ages primarily consumed fish prey regardless of the month or year. Each age category of striped bass selected for one or more species of prey from the suborder Clupeoidei. Age‐1 striped bass selectivity of Alosa spp. generally increased with the progression of each sampling season, whereas selectivity for Atlantic menhaden, Menidia spp., and yellow perch decreased over time within each season. Striped bass of all ages displayed strong selection for Atlantic menhaden and strong selection against spiny‐rayed fish prey. Striped bass displayed selection for specific prey, although the mechanisms responsible for selection appear to vary through time and may differ for different prey types. Striped bass either displayed neutral size selectivity or selected for relatively small prey. The mean and maximum sizes of fish prey increased with increases in striped bass size, but the minimum prey size changed little. Our results of seasonal and age‐specific changes in selectivity will be valuable for modeling the impact of striped bass predation on resource prey species.
We examined diet, dietary niche width, diet overlap, and prey size–predator size relationships of blue marlins Makaira nigricans, dolphinfish Coryphaena hippurus, yellowfin tuna Thunnus albacares, ...and wahoos Acanthocybium solandri caught in the western North Atlantic Ocean during the Big Rock Blue Marlin Tournament (BRT) in 1998–2000 and 2003–2009 and dolphinfish captured outside the BRT from 2002 to 2004. Scombrids were important prey of blue marlins, yellowfin tuna, and wahoos; other frequently consumed prey included cephalopods (for yellowfin tuna and wahoos) and exocoetids (for yellowfin tuna). Dolphinfish diets included exocoetids, portunids, and conspecifics as important prey. Blue marlins and wahoos consumed relatively few prey species (i.e., low dietary niche width), while dolphinfish had the highest dietary niche width; yellowfin tuna had intermediate niche width values. Maximum prey size increased with dolphinfish size; however, the consumption of small prey associated with algae Sargassum spp. occurred across the full size range of dolphinfish examined. Most interspecific diet overlap values with dolphinfish were not significant; however, blue marlins, yellowfin tuna, and wahoos had significant diet overlap due to their reliance on scombrid prey. Prey types found in blue marlins, dolphinfish, and wahoos were more consistent among BRT years than prey found in yellowfin tuna. The prey of yellowfin tuna and wahoos collected during BRT years correlated with historic (early 1980s) diet data from North Carolina, the Gulf of Mexico, and the Bahamas. Based on principal components analysis, diets from several oceans clustered together for blue marlins, dolphinfish, yellowfin tuna, and wahoos. Although differences were found, the diets of each predator were largely consistent both temporally (e.g., over the past three decades in the Gulf Stream) and spatially (among oceans), despite potential effects of fishing or environmental changes.
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