Legal-sized Fish Research Articles

Low catchability limits the effect of warm-water catch-and-release mortality on muskellunge

Catch-and-release (C&R) has become a popular practice in many fisheries, but especially in muskellunge Esox masquinongy fisheries where voluntary release rates of legal-sized fish have approached 100%. Because muskellunge are a coolwater species, muskellunge anglers and biologists have expressed concerns regarding the population-level effects of additional mortality from C&R during periods of elevated water temperatures. Therefore, we used a combination of a radio telemetry study and individual-based growth model simulations to evaluate the effects of warm-water C&R mortality on the length potential of muskellunge in the James River, Virginia. We implanted radio transmitting tags in muskellunge ≥ 650 mm in winter 2020 (N = 45) and 2021 (N = 50) to monitor fates of fish that were subsequently caught and released during the warm-water period (July – August). Twelve tagged fish were caught and released in the warm-water period, of which four died (33%). Despite a high rate of mortality compared to studies conducted during cooler temperatures, our simulations indicated that a closed season during the warm-water period on the James River would result in little to no increase in the proportions of muskellunge reaching preferred (≥1020 mm) and memorable (≥1140 mm) size classes because (1) thermally stressed fish were not susceptible to angling, and (2) growth potential beyond the memorable size class is currently limited in the James River. Given the growing popularity of muskellunge angling in the southern portion of their distribution and projected increases in water temperature throughout the muskellunge’s distribution, results from this study will provide managers with the information necessary for developing more comprehensive muskellunge management plans.

Baited video, but not diver video, detects a greater contrast in the abundance of two legal-size target species between no-take and fished zones

Inherent differences between baited remote video versus diver-operated video survey methodologies may influence their ability to detect effects of fishing. Here, the ability of no-take zones (NTZs) to provide protection for legal-sized fish from targeted species within the Ningaloo Marine Park (NMP) was assessed using both baited remote underwater stereo-video (stereo-BRUV) and diver-operated stereo-video (stereo-DOV). The relative abundance of legal-sized individuals of three recreationally targeted fish species, spangled emperor Lethrinus nebulosus, chinaman cod Epinephelus rivulatus and goldspotted trevally Carangoides fulvoguttatus, were examined using both methodologies inside and outside six NTZs across the NMP. Stereo-BRUVs found positive effects of protection on the relative abundance of legal-size C. fulvoguttatus and L. nebulosus in NTZs. Stereo-DOVs, however, did not detect any differences in relative abundances and sizes of these species between areas opened and closed to fishing. These contrasting results suggest that choice of sampling methodology can influence interpretations of the ability of NTZs to provide adequate levels of protection for target species. Our results suggest that stereo-BRUVs are a superior technique to stereo-DOVs for assessing the effectiveness of no-take zones for protection of fishery target species, reflecting bait attraction and an absence of diver influence on fish behaviour.

Golden perch (

Context Intermittent rivers make up more than 50% of the world’s rivers. Refuge waterholes in these systems are critical for survival of fish populations. Aim This study investigated the effect that angling pressure imparts on native fish within refuge waterholes. Methods Golden perch (Macquaria ambigua) size structure was analysed in eight refuge waterholes across three catchments of the northern Murray–Darling Basin. Waterhole characteristics were recorded, with town proximity or remoteness being adopted as a surrogate variable for angling pressure. Key results Remoteness was found to be significantly correlated with median length, biomass, and proportion of legal-sized fish, but not with fish density. Sampling occurred after widespread connective flows, and the strength of remoteness as a predictor of median length suggests that redistribution of legal-sized golden perch on these flows was minimal. Legal-sized fish were poorly represented in the length–frequency distributions of near-town waterholes, and smaller size classes were well represented in most waterholes. Conclusion This study suggests that populations of golden perch in refuge waterholes near towns face significant angling pressure, with impacts on size structure at a local level. Implications These findings may have wider implications for the long-term resilience of the species.

Biotelemetry based estimates of greater amberjack (Seriola dumerili) post-release mortality in the northern Gulf of Mexico

The Gulf of Mexico greater amberjack (Seriola dumerili) stock has been designated as “overfished” by the National Marine Fisheries Service and is currently under a rebuilding plan. Its fishery in the Gulf of Mexico is dominated by recreational landings, where 75% of the total recreational catch are regulatory discards; as such, uncertainty regarding the post-release mortality rate represents a data deficiency in the stock assessment. To determine post-release mortality, a combination of acoustic and pop-up satellite archival transmitting (PSAT) tags were used to monitor the release fate and depth-use of greater amberjack. Thirty-six greater amberjack were tagged with acoustic transmitters at two sites in the northern GOM and monitored for up to 30 days. Sublegal-sized fish (n = 18) ranged from 591 to 740 mm FL (mean = 674.6 ± 40.6 SE) and legal-sized fish (n = 18) ranged from 768 to 1081 mm FL (mean = 871.3 ± 77.5 SE). All 36 fish were detected in the array after release. Based on examination of time series depth profiles, post-release mortality was estimated to be 18.8% ± 6.9%, strikingly similar to the estimate used in the most recent stock assessment. Stepwise model selection using AIC identified the Cox proportional hazards model containing only release condition as the most parsimonious model to predict post-release mortality. Despite differences in depth between the two tagging sites, fish showed slight, but consistent, size-specific segregation patterns. Our findingsadd to a body of literature demonstrating that biotelemetry is an effective tool in catch and release mortality studies, and provide best practices that can aid in the recovery of this stock.

Effects of sex-specific fishing mortality on sex ratio and population dynamics of Gulf of Mexico greater amberjack

The US Gulf of Mexico stock assessment of greater amberjack Seriola dumerili assumes a 1:1 male:female sex ratio. However, the observed sex ratio in the landed catch is 1:1.8, and for fish >1 m fork length is 1:2.4. To theoretically explore whether this female-skewed sex ratio may arise due to differential fishing mortality between the sexes, we used a sex-specific age- and size-based model to investigate how different fishing mortality rates could create a female-skew in the landed catch as well as its subsequent effects on reproductive potential. When fishing mortality rates in the model were equal between the sexes, the sex ratio of the landed catch was approximately 1:1 for all legal-sized fish, and approximately 1:2.4 for fish >1 m FL. However, reproductive potential decreased in comparison to the corresponding scenario with equal fishing mortality rates when fishing mortality rates between the sexes were changed to create the 1:1.8 sex ratio observed in the landed catch. This modeling study demonstrates one possible route that could explain the female-skewed sex ratios observed in the landed catch, and indicates that sex ratio values other than 1:1 should be considered in future stock assessments for Gulf of Mexico greater amberjack.

Using generalized linear models to estimate selectivity from short-term recoveries of tagged red drum Sciaenops ocellatus: Effects of gear, fate, and regulation period

Estimating the selectivity patterns of various fishing gears is a critical component of fisheries stock assessment due to the difficulty in obtaining representative samples from most gears. We used short-term recoveries ( n = 3587) of tagged red drum Sciaenops ocellatus to directly estimate age- and length-based selectivity patterns using generalized linear models. The most parsimonious models were selected using AIC, and standard deviations were estimated using simulations. Selectivity of red drum was dependent upon the regulation period in which the fish was caught, the gear used to catch the fish (i.e., hook-and-line, gill nets, pound nets), and the fate of the fish upon recovery (i.e., harvested or released); models including all first-order interactions between main effects outperformed models without interactions. Selectivity of harvested fish was generally dome-shaped and shifted toward larger, older fish in response to regulation changes. Selectivity of caught-and-released red drum was highest on the youngest and smallest fish in the early and middle regulation periods, but increased on larger, legal-sized fish in the late regulation period. These results suggest that catch-and-release mortality has consistently been high for small, young red drum, but has recently become more common in larger, older fish. This method of estimating selectivity from short-term tag recoveries is valuable because it is simpler than full tag-return models, and may be more robust because yearly fishing and natural mortality rates do not need to be modeled and estimated.

Mercury concentrations in red drum, Sciaenops ocellatus, from estuarine and offshore waters of Florida

Dorsal muscle tissue from 712 red drum, Sciaenops ocellatus, from Florida waters were analyzed for total mercury content. Mercury levels detected in these red drum varied but in most study areas were usually lower than regulatory threshold guidelines. Total mercury levels in individual fish from all study areas ranged from 0.020 to 3.6 ppm (wet weight). Total mercury levels detected in red drum from the Florida Keys-Florida Bay area were often higher than those in fish from all other estuarine study areas. Positive relationships between total mercury levels and fish size (length and weight) and fish age were observed in most Florida study areas, indicating that mercury levels tend to increase over time as red drum grow. The majority of large, mature red drum examined contained mercury levels greater than the 0.5-ppm threshold level set by the Florida Department of Health (DOH). Approximately 94% of all adult red drum from offshore waters adjacent to Tampa Bay contained mercury levels greater than or equal to the 0.5-ppm threshold level, and 64% contained levels greater than or equal to the DOH 1.5-ppm “no consumption” level. All fish from this area with mercury levels greater than 1.5 ppm were large individuals (⩾670 mm SL). Eight percent of legal-size red drum from Florida waters contained total mercury levels greater than or equal to the 0.5-ppm threshold level. The majority (52%) of these legal-size fish greater than or equal to 0.5 ppm were from the Florida Keys-Florida Bay area. In the Florida recreational fishery, the current maximum size limit for this species is an effective filter that prevents humans from consuming those red drum with the greatest likelihood of containing high mercury levels.

Reducing the mortality of discarded undersize sand whiting Sillago ciliata in an estuarine seine fishery

A field experiment was done to determine the effects of mesh size in the bunt and codend of an estuarine beach-seine net on the meshing (gilling) and discarding of undersize sand whiting Sillago ciliata (Sillaginidae). Four mesh sizes were examined: 45 mm, 50 mm, 57 mm and 64 mm, in an alternate-haul experiment in the Clarence River, New South Wales, Australia. A laboratory experiment was also done to determine the mortality of sand whiting after becoming meshed in seine nets. The currently allowed mesh size (50 mm) catches a large proportion of undersize sand whiting that become meshed in the netting and are subsequently discarded. The laboratory experiment showed that ~40% of these fish may die within a few weeks whereas no unmeshed fish die. In contrast, the 57 mm mesh size meshed few undersize sand whiting yet retained almost the same number of legal-sized fish as the 50 mm mesh. Hence, the maximum mesh size allowed in the bunts of nets used in this fishery should be raised to 57 mm to allow the escape of large numbers of undersize sand whiting that are currently being caught, meshed and discarded in a condition that leads to significant mortality.

Characteristics of Commercially Harvested Channel Catfish From Areas of the Mississippi River Along Illinois: Commercial Harvest and the 15.0—in Minimum Length Limit

ABSTRACT We examined commercially harvested channel catfish from Mississippi River Pools 13, 19, 25, and an unimpounded area near Chester, IL to determine age, growth, fecundity, and population sizes. Most fish harvested from Pools 13 and 19 were ages 4–6, while fish from Pool 25 and Chester were mainly ages 6–8. Fish grew fastest in Pool 19, followed by those from Pool 13, Chester, and Pool 25, respectively. Several year classes were well represented in the harvest in each study area since enactment of the 15.0-in limit, thus reducing the dependency of harvests on 1 or 2 year classes. Approximately 60–70% of channel catfish were sexually mature at 15.0 in. Mean fecundity estimates were generally highest for Pool 19 fish and lowest for Pool 25 fish, ranging from 5,300 to 37,000 eggs. Eggs were produced as early as age 3, and production peaked at ages 6–8 (> 18.0 in long). Population estimates for legal-size fish (> 15.0 in) ranged from 262,000 to 477,300 in Pool 13, while estimates were considerably highe...

Migration patterns in barramundi, Lates calcarifer (Bloch), in Van Diemen Gulf, Australia, with estimates of fishing mortality in specific areas

About 4000 barramundi were tagged in the four major river systems in Van Diemen Gulf in 1977/1978 to determine migration patterns and exchanges of fish between rivers, and to estimate fishing mortality. Some exchange of barramundi between rivers occurred. A general seaward migration of mature fish into coastal areas was associated with spawning. There was no evidence of a movement of spent fish back to inland waters after spawning. The overall recovery rate of legal-sized fish (≥58 cm TL) was highest in the Mary River (19%), followed by the East Alligator River (12%), South Alligator River (8%) and West Alligator River (2%). Annual fishing mortalities for specific localities ranged from 0.15 for inland waters well outside the commercial fishing grounds to 0.45 in coastal waters within the commercial fishing grounds, reflecting the general seawards movement of fish from inland areas and their subsequent recruitment to the commercial fishery.

A History and Evaluation of Regulations for Brook Trout and Brown Trout in Michigan Streams

Abstract Since establishment of the Board of Fish Commissioners in 1873, the trend in Michigan trout fishing regulations has been toward more restrictive and complex laws. Major scientific investigations concerning the effectiveness of various types of regulations began in 1945. Those studies indicated that a minimum size limit was the most effective regulation for controlling exploitation of trout. In this study, minimum size limits for brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) in Michigan streams were evaluated through mathematical modeling. Minimum size limits ranging from 152 to 229 mm were tested for brook trout and from 152 to 305 mm for brown trout. Catch-and-release (no-kill) regulations were also simulated for both species. Maximum yield in numbers and weight of trout harvested (legal-size fish killed) was obtained at a 152-mm minimum limit for both species. Yield in numbers and weight of trout caught and released (sublegal fish returned to water alive) increased as size ...

Comparison of the effects of different linefishing methods on catch composition and capture mortality of South African temperate reef fish

The effects of hook size, bait type, water depth and fishing effort on the selectivity and capture mortality of reef fish were investigated in a standardised fishing experiment on the temperate south coast of South Africa. A total of 2 406 fish was caught at 273 stations, distributed according to a random-stratified design. Generalised linear models separated the influences of environmental factors such as depth, temperature and season from the effects of fishing methods on catch rates and capture mortality. Dominant reef predators and larger individuals within species were more frequently caught on large hooks and sardine Sardinops sagax bait. The main cause for capture mortality was gut-hooking, aggravated by increased capture depth. Large roman Chrysoblephus laticeps were more frequently gut-hooked than small individuals. More roman were caught early in the fishing session and the average size of captured roman increased slightly during fishing sessions. The selection of legal-sized target fish can be increased by about 23% and immediate capture mortality of undersized fish can be reduced by 50% by using large hooks and sardine bait and by fishing for less than one angler-hour per station in water shallower than 20m. The results are useful for planning fisheries independent catch per unit effort surveys and for developing rules for catch-and-release competitions.

Absorption and Retention of Organic Mercurials by Rainbow Trout and Chinook and Sockeye Salmon

The Food and Drug Administration has established zero tolerance for mercury in foodstuffs because of its potential hazard to human health. This limit may be modified if further studies indicate permissible levels. These experiments indicate that mercurials used as therapeutics and prophylactics for fish diseases can be absorbed and retained by fish for prolonged periods, and that legal-size wild fish may ingest enough mercury-contaminated fingerlings to accumulate relatively high levels of mercury. Therefore, legal-size hatchery fish treated with mercurials or wild fish that have eaten mercury-contaminated fingerlings may be a public health hazard. 6 tables.

The Relative Efficiency of Nylon and Cotton Gill Nets for Taking Lake Trout in Lake Superior

The change from cotton to nylon twine for gill nets in 1949–52 resulted in a sharp increase in the efficiency of the most important gear used for taking lake trout in Lake Superior, and, consequently, biased estimates of fishing intensity and abundance severely.From early May to the end of September 1961, short gangs (2000 or 4000 linear feet) of cotton and nylon nets were fished in parallel sets for lake trout. A total of 343,000 feet of gill netting was lifted. Nylon nets were 2.25 times as efficient as cotton nets for taking legal-sized fish and 2.8 times as efficient for undersized lake trout. The average lengths of legal, undersized, and all lake trout taken in nets of the two materials did not differ greatly. The percentage of the catch which was undersized (less than 1.25 lb, dressed weight) was 20.8 in nylon nets and 17.7 in cotton. The relative efficiency of cotton and nylon nets showed no trend during the season. The efficiency ratio determined in this study was closely similar to that obtained by earlier workers.Correction of estimates of fishing intensity and abundance for the greater efficiency of the nylon nets used since 1951 has not been attempted. The drastic decline of the lake trout fishery has forced fishermen to make changes in fishing practices in the past few years that cause new bias of an unknown extent to estimates of fishing intensity.

The near Extinction of Lake Trout in Lake Michigan

After the collapse of the commercial fishery for lake trout (Salvelinus namaycush) in Lake Michigan in the late 1940ˈs, the further decline of the population was traced by records of numbers of small lake trout (mostly 11 to 16 inches in total length and 3 to 5 years old) caught in small-mesh nets of the chub (Coregonus \[= Leucichthys\] spp.) fishery. By 1951 the estimated abundance of these lake trout in lower Lake Michigan was only about 4 percent of their abundance prior to the invasion of the sea lamprey (Petromyzon marinus). This remnant of the population declined severely in subsequent years to a point near extinction by 1955. In April-July 1955 only 8 lake trout were caught in 5 1/2 million linear feet of gill net. Statistics of the lake trout and chub fisheries in State of Michigan waters of Lake Michigan for the years 1929–1954 give no indication that the destruction of small lake trout in the chub fishery had any effect on the later abundance of lake trout of commercial size, or that this destruction was a significant factor in the collapse of the lake trout fishery. Lake trout were brought near extinction by lethal attacks of the sea lamprey and by the near or perhaps complete failure of natural reproduction in 1949 and subsequently. Comparisons in 1949 and 1950 of numbers of legal-sized lake trout caught in large-mesh nets with numbers of small fish taken in chub nets showed that both large and small lake trout declined over the same period, and that by these years the decline may have been greater among small than among legal-sized fish.

Estimation of Fish Populations in Michigan Lakes

Fish population estimates, using trap nets in the Petersen mark-and-recapture procedure, were made during 1948, 1949, and 1950 on Sugarloaf Lake in Washtenaw County and during 1950 on Fife Lake in Grand Traverse County, Michigan. The nets were of two sizes: 3-foot and 6-foot. The lake acreages are 180 and 575, respectively. The important fish species were bluegill, pumpkinseed sunfish, yellow perch, largemouth bass, smallmouth bass, black crappie, northern pike, yellow and brown bullheads, and warmouth. The study was limited to fish over 6 inches in length. In four separate netting periods, 17,887 fish (approximately half bluegills) were marked by fin clipping and released, and 2,991 of these (17 percent) were recaptured. Distinctive markings were used for fish from two halves of each lake, and recaptures were tabulated accordingly. Marked fish, liberated at a common release station near the center of the lake, showed a tendency to return to the same half of the lake where marked; but the amount of this “homing” was not sufficient to invalidate the population estimations. Distinctive marking for two groups of stations, separated systematically according to even and odd numbers in series, gave returns which showed no marked tendency for fish to return to their home trap-net site. The three separate estimations of populations of legal-size fish in Sugarloaf Lake, computed by the Schumacher and Eschmeyer formula, gave 17,648 fish for the fall estimate of 1948, a total of 15,531 fish for the spring estimate in 1949, and 22,178 fish in the spring of 1950. These totals, correlated with the numbers of trap-net stations on which the estimates were based (30, 20, and 40, respectively) suggest, by extrapolation, that the true population figure is something less than 30 thousand. The average computed total for the 3 years was 18,452 fish, or 102 fish and 43.1 pounds per acre. Estimations by the Schnabel formula gave totals which were generally a little higher than by the Schumacher and Eschmeyer formula. For Fife Lake the estimated total population was 99,056 fish or 172 fish of 62.3 pounds per acre. In both lakes the bluegill made up over half of the totals. Records of marked and unmarked fish in anglersˈ creels immediately following the trap netting provided another basis for estimating the fish populations in Sugarloaf Lake in 1949 and 1950. Such estimates were about double the estimates based on trap-net recaptures. The reason for the difference was not determined.

A Summary of Experiments in Michigan Lakes on the Elimination of Fish Populations with Rotenone, 1934–1942

Abstract During the period 1934–1942, 32 lakes in Michigan were treated with rotenone to remove or reduce unwanted fish populations, and an attempt to recover the entire fish population was made on 18 of them. The majority of these lakes were not supporting a desirable or normally growing fish population at the time they were treated. They were mostly small, all less than 22 acres, and included lakes whose waters ranged from very soft to very hard, from acid to alkaline, and from shallow to very deep. In productivity, as measured by the standing crop of fish recovered, these lakes ranged from 10.0 to 194.5 pounds per acre. The lakes averaged 58.5 pounds of fish per acre of which 18.2 pounds were legal-sized game fish. The hard-water lakes were, in general, more productive than the soft-water lakes and the warm-water lakes more productive than the trout lakes.

Further Results from Spring and Fall Plantings of Legal-Sized, Hatchery-Reared Trout in Streams and Lakes of Michigan

Further tagging experiments in Michigan with spring and fall plantings of brook trout (Salvelinus f. fontinalis, brown trout (Salmo trutta), and rainbow trout (Salmo gairdnerii irideus) from which recoveries were made during the 1942 trout season confirmed the conclusion that spring release of adult or near adult hatchery-reared brook trout and rainbow trout is more desirable than the fall planting of fish of a similar size. In some instances fall stocking of brown trout may furnish as good fishing in the following seasons as does spring planting. Recoveries of planted fish past the first season of availability ranged from 0.0 to 2.5 per cent in the second season and from 0.0 to 0.5 per cent in the third season. In either spring or fall planting of legal-sized fish, no advantage was gained by scattering the fish widely over the stream areas stocked. Eighty five per cent or more of the planted trout recovered were caught within 10 miles of the point of release, regardless of the season or method of planting. Brown trout moved the least and rainbow trout the most. About one-fourth of the brook trout tended to move 3 to 10 miles downstream, and the majority of the remainder were caught within 3 miles of the locality of release. More rainbow trout than any other species were recaptured 10 or more miles from the point of release. Fall plantings of adult brook trout in lakes were recovered at the rate of 56.7 per cent (range, 13.0 to 88.1 per cent). Unfortunately, a small percentage of the anglers removed an average of 89.4 per cent of the total catch during the opening weeks of the trout season. The average recovery from two spring plantings of brook trout in East Fish Lake in Michigan was 68.5 per cent. A brief review of the literature substantiates the conclusions reached as a result of the Michigan experiments. Differences in experimental procedure are pointed out, and some reasons are offered for the failure of fish planted in streams in the fall to survive the winter season.

Survival, Population Density, Growth, and Movement of the Wild Brown Trout in Crystal Creek

Abstract A portion of the data accumulated in a 4-year study of the trout of Crystal Creek, New York State, is reported. An annual population inventory of the same 13 sample sections of the stream each September for 4 years provided information on survival, density of fish, growth, movement, and other factors. The percentage survival of the young brown trout of the year (age-group 0) in later years was found to be as follows: Second year (age-group I), 24.1; third year (age-group II), 11.0; fourth year (age-group III), 5.49; fifth year (age-group IV), 1.25; sixth year (age-group V), 0.48. The trout were subject to angling, which accounted for about 15 per cent of the yearly losses of the legal-sized fish. A considerable mortality of the larger-sized trout, for which the cause could not be determined, was observed each year during July. Hatchery fingerlings planted in September survived to the following September at rates varying from 0.25 per cent to 6.3 per cent (the latter figure is the more reliable). ...

Food of Some Lake St. Marys' Fish with Comparative Data from Lakes Indian and Loramie

With the development of the new science, Fish Management, comes the need of additional information concerning the lives and habits of the fish in our fish populations. Numerous studies have been made on all the species mentioned, but so far as is known to the author, no food studies have been made of the fishes of the lake under consideration. Fish Management principles involve the building up of an increasing food supply to support and mature a greater population of legal-sized fish. With the above thought in mind, the ensuing studies were made.