Spring Fishery Research Articles

Hard to Manage? Dynamics of Soft-Shell Crab in the Newfoundland and Labrador Snow Crab Fishery

Capture of recently molted soft-shell crab in the Newfoundland and Labrador (NL) snow crab (Chionoecetes opilio) fishery is undesirable due to resource wastage associated with low meat yield and supposed high mortality rates upon discard. This study is intended to formalize best-practice management advice for avoidance of soft-shell crab in the fishery. The study investigates factors affecting soft-shell incidence in the catch across a large geographic stock range encompassing dynamic habitat and contrasting harvest rate strategies. The results demonstrate an interaction between seasonality and harvest rate in governing soft-shell crab levels in the fishery. Greatest potential for high soft-shell incidence occurs in late-spring or summer (June–July) fisheries in warm water populations subjected to heavy fishing pressure, with warm water populations shown to be associated with earlier molting periods. The study concludes that the optimal time to harvest snow crab is during winter or early spring, and advises that wherever winter or early spring fisheries are not possible, a best-practice management strategy is to minimize wastage by maintaining a strong residual biomass of large hard-shell males in the population at all times. This strategy is easily enabled by consistent application of low exploitation rates.

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.

Increased mortality of harvested eastern oysters (Crassostrea virginica) is associated with air exposure and temperature during a spring fishery in Atlantic Canada

In Prince Edward Island, the spring oyster fishery occurs from early May to mid-July. During this time, oysters may be harvested and held for multiple days by harvesters before being brought to oyster processors, who then relay them in seawater at leased sites. Over the past decade, however, processors have reported high mortalities of relayed catch during July. We investigated duration of air exposure as a potential driver for the high July mortalities reported by oyster processors. Wild oysters were removed from fishing beds in June and July 2017 and handled to mimic techniques used by harvesters. After removal, the oysters were exposed to atmospheric conditions (air) for 0, 24, 48, 72, or 96 h and mortality was quantified. The oysters were then placed at a holding site for 60 days and mortality was quantified on days 7, 14, 30 and 60, and condition index was measured on remaining oysters from each air exposure treatment. Increased mortality was associated with increased air exposure duration, and this effect was most pronounced during July. Oysters exposed to air for 72–96 h in June experienced mortality rates of 4–11%, while the same air exposure duration in July yielded mortality rates four times higher than in June (16–44%). Most of the associated mortality occurred during air exposure and within 7 days of placing oysters at the holding site. Condition index was also lower in July; however there was no evidence that oysters had spawned. Higher mortalities and lower condition indices in July were associated with higher average air and seawater temperatures (both ∼3 °C higher than June). These results ultimately suggest that increased air exposure can result in substantial mortality of PEI oysters fished in July, and corroborate the reports of high July mortalities from oyster processors.

Evaluation of angler reporting accuracy in an off‐site survey to estimate statewide steelhead harvest

AbstractAccuracy of angler‐reported data on steelhead, Oncorhynchus mykiss (Walbaum), harvest in Idaho, USA, was quantified by comparing data recorded on angler harvest permits to the numbers that the same group of anglers reported in an off‐site survey. Anglers could respond to the off‐site survey using mail or Internet; if they did not respond using these methods, they were called on the telephone. A majority of anglers responded through the mail, and the probability of responding by Internet decreased with increasing age of the respondent. The actual number of steelhead harvested did not appear to influence the response type. Anglers in the autumn 2012 survey overreported harvest by 24%, whereas anglers in the spring 2013 survey under‐reported steelhead harvest by 16%. The direction of reporting bias may have been a function of actual harvest, where anglers harvested on average 2.6 times more fish during the spring fishery than the autumn. Reporting bias that is a function of actual harvest can have substantial management and conservation implications because the fishery will be perceived to be performing better at lower harvest rates and worse when harvest rates are higher. Thus, these findings warrant consideration when designing surveys and evaluating management actions.

Low prevalence of splenic mycobacteriosis in migratory striped bass Morone saxatilis from North Carolina and Chesapeake Bay, USA

Mycobacteriosis is a chronic bacterial disease causing an ongoing epizootic in striped bass Morone saxatilis in Chesapeake Bay, U.S.A. Prevalence of disease is high in pre-migratory fish, and multiple species of Mycobacterium spp. have been isolated. However, prevalence of mycobacteriosis in the coastal migratory population is unknown and is of concern to multiple coastal states, as disease-related mortality may impact the long-term health of the population. Histological examinations of spleens collected from fish caught by recreational anglers during the winter fishery in coastal North Carolina (2005-2006, n=249) and during the spring fishery in Chesapeake Bay (2006, n=120) indicated a low prevalence of mycobacteriosis (6.8% of all fish examined) in comparison to smaller, pre-migratory Chesapeake Bay fish. Genus-level PCR and subsequent sequencing of the 16-23S intergenic transcribed spacer (ITS) region revealed that all bacteria were phylogenetically related, but species is unknown. Location of survey, gender of fish, and total length of fish had no significant effect on prevalence of mycobacteriosis, parasitic granulomas, or the density of splenic granulomas (p > 0.05). These results may indicate that either granulomas resolve after Chesapeake Bay fish enter the coastal migratory population, or that there is disease-related mortality among pre-migratory Chesapeake Bay fish.

Sex Ratios of Black Crappies Harvested during Spring Fisheries on Two Minnesota Lakes: Are Males in the Majority?

AbstractSex‐selective fishing mortality can alter the demographics and life history patterns of fish populations, yet the extent of this mortality is rarely investigated in harvest‐oriented recreational fisheries. Potential differences in habitat use between sexes and nest‐guarding behavior suggest that male black crappies Pomoxis nigromaculatus could dominate angler harvest during spring fisheries. We examined the potential for male‐dominated harvest in spring (late April to mid‐June) recreational fisheries for black crappies occurring on two north‐central Minnesota lakes. In the three spring fisheries we examined, males represented between 45% and 57% of all black crappies harvested by anglers, but sex ratios (expressed as the percentages of males) did not significantly deviate from 1:1. However, a temporal pattern in sex ratios was observed on Lake Hubert, where female black crappies dominated angler harvest before 19 May in both 2005 and 2006 (41–42% male) while the harvest on or after 19 May was dominated by males (69–75% male); this shift appeared to coincide with peak nesting periods. In fall electrofishing samples, the sex ratios of black crappies that had been exposed to exploitation during spring fisheries (i.e., fish age 4 and older) did not significantly deviate from 1:1, suggesting that total annual mortality rates were similar between sexes. The sex ratios of black crappies harvested by anglers during spring can vary within and among lakes and will not always be skewed toward male fish. Estimating population sex ratios and the sex ratio of black crappies harvested by anglers may improve our understanding of the effects of exploitation on crappie populations, particularly when fishing intensity during nesting is high and nests are easily located by anglers.

Protecting window‐size female American lobster, Homarus americanus, to increase egg production

A new conservation measure aimed at protecting the larger broodstock (females with a carapace length between 115 and 129 mm, i.e., window‐size females, WSF) to enhance egg production was implemented in 2003 for the American lobster (Homarus americanus) fishery in the southern Gulf of St. Lawrence, Canada. To assess the effectiveness of this new measure, a tagging project was carried out between 2004 and 2007 in the Hillsborough Bay area with the collaboration of local harvesters. Based on a single mark‐recapture Petersen model, the estimated catch rates of WSF not carrying eggs under the abdomen in the study area varied between 40% and 53%. The catch‐per‐unit‐effort (animals per 100 traps) of both berried (egg‐bearing) and non‐berried WSF increased from 0.2 to 0.8 and 1.0 to 1.6, respectively, between 2004 and 2007. Based on the estimated number of non‐berried WSF in the population observed during the spring fishery between 2004 and 2007, the potential total egg production for WSF was estimated at 1.1 billion in the study area. From this total, 515 million eggs would have been produced by WSF directly protected by the conservation measure, i.e., females that would have been harvested if not for the new regulation. Finally, the contribution of berried WSF to the annual egg production in the study area increased from 4% to 23% between 2003 and 2007 based on the at‐sea sampling programme and the fecundity curve. WSF that represented 10% of the total berried female population in 2007 contributed 23% of the annual egg production. Hence, the protection of WSF seems to be an effective conservation measure to increase egg production based on the catch‐per‐unit‐effort and egg production.

The influence of wind and temperature on the catch rate of the American lobster (Homarus americanus) during spring fisheries off eastern Canada

AbstractThe effects of wind and temperature on catch rate of American lobster (Homarus americanus) in the Baie des Chaleurs and off Cape Breton Island in Eastern Canada were investigated. Data on lobster catch and the number of trap hauls were available through a fishermen's volunteer logbook program, bottom temperatures were measured from thermistors either moored nearby or placed inside lobster traps and wind measurements were obtained from local airports. In the Baie des Chaleurs and off the east coast of Cape Breton, a positive and significant correlation was found between the mean temperature change during the 24 h prior to the traps being hauled and the change in the average catch of lobsters per trap haul. Catch rates rose with increasing bottom temperatures and fell with declining bottom temperatures. Higher correlations between changes in temperature and catch rates occurred at sites where the temperature variance was greater. The short‐term fluctuations in lobster catch rates corresponding to temperature changes are hypothesized to result from behavioral changes affecting lobster activity. In both study areas, the large temperature variability was mainly forced by alongshore winds producing upwelling and downwelling, consistent with a classical Ekman response. The effect of the winds on lobster catch is shown to be principally due to their influence on ocean bottom temperatures. Along the south coast of Cape Breton, no relationship was found between catch rates and either temperature or wind, perhaps because lower lobster abundance resulted in a lower signal‐to‐noise ratio. The results of this study qualitatively support the observations by fishermen of a wind‐induced effect on lobster catch rates.

Use of Traditional Ecological Knowledge to Reduce Striped Bass Bycatch in the Currituck Sound White Perch Gill‐Net Fishery

AbstractThe gill‐net fishery for white perch Morone americana in upper Currituck Sound, North Carolina, currently is regulated by season, mesh‐size, and net tending restrictions primarily intended for reducing the bycatch of striped bass Morone saxatilis. The fall fishery (September– December) cannot use small‐mesh nets, and fishers must tend nets at all times within a distance of 91.4 m. The spring fishery (January–April) also has small‐mesh restrictions, but fishers can leave nets unattended. Commercial fishers are concerned about these restrictions. We examined these concerns by designing a study in which randomly deployed gill nets were paired with nets set at sites chosen by a commercial fisher based on traditional ecological knowledge of the region. The commercial fisher reduced bycatch of striped bass while maintaining catches of white perch. Marketable quality (i.e., average size) of white perch was not significantly different between random sets and commercially designated sets. Most of the total catch (95%) and a majority of striped bass (64%) were caught alive. The number of live captures was inversely correlated with water temperature and positively correlated with oxygen content. Management recommendations include initiation of similar gill‐net studies both within Currituck Sound and statewide for comparison of results, development of a fisher questionnaire to ascertain experience level, and establishment of observer coverage to confirm the results presented here.

Rescinding a 254-mm Minimum Length Limit on White Crappies at Ft. Supply Reservoir, Oklahoma: The Influence of Variable Recruitment, Compensatory Mortality, and Angler Dissatisfaction

A 254-mm minimum length limit on crappies Pomoxis spp. was implemented on January 1, 1990, in Ft. Supply Reservoir, Oklahoma, to improve population size and age structure and angler catch rates but was rescinded 6 years later because of angler complaints. Before the regulation, the population was characterized by fast-growing and short-lived white crappies P. annularis; the spring fishery was supported by age-2 fish. Size structure fluctuated widely before the length limit was implemented, ranging from 1% to 40%, but stabilized after the length limit, exceeding 20% in 5 of the next 6 years. Age structure (percent age 3 and older) never exceeded 10% before the length limit, was greater than 10% the first 4 years after the length limit was imposed, and then declined to less than 10% in 1994–1995. Before the length limit, estimated conditional natural mortality was 45% and exploitation was 40%. Survival from age 1 to age 2 averaged 27% before the length limit and did not change substantially following its implementation. Abundance of quality-size (200–249 mm) and preferred-size (>250 mm) white crappies increased after the length limit was imposed. Angler catch rates increased following the regulation, but harvest rates were unchanged and harvest by number and yield declined. A Beverton–Holt equilibrium yield model, fitted using the pre-length-limit data, accurately predicted a reduction in yield. It was apparent from this study that typical fish population metrics are insufficient for managing a crappie fishery. Angler effort declined dramatically after the length limit was imposed, and vocal anglers registered their displeasure with their inability to harvest crappies. Reservoir-specific or lake-specific human dimensions data are also needed to properly assess angler desires before regulations are imposed. Managers should be flexible with regulations and be responsive to changing angler and fishery needs.

Reduced Catch of Under-Sized Cod (Gadus morhua) in Longlining by Using Artificial Bait

Three sizes of artificial bait incorporating shrimp flavour into polyurethane foam were compared with natural shrimp bait of the size used in commercial longlining. Fishing trials were conducted during the spring fishery for Atlantic cod (Gadus morhua) off the coast of Northern Norway. The small artificial bait gave almost the same catch rate as natural shrimp bait, whereas artificial baits of larger sizes compared poorly. The length distribution of the catch was influenced by both bait type and bait size. Fewer small cod were caught on the artificial baits. There was no difference in the number of large cod. Mean cod length was therefore higher on the artificial baits and increasing the artificial bait size accentuated the difference. These effects are explained by different preferences with regard to prey species and size between small and large cod. The size selective effects of bait type and bait size are discussed in relation to conservation aspects.

Director's Report

The various researches detailed in my last Report, which are being conducted by the Association's Naturalists, have been continued during the winter. Mr. Garstang has been chiefly occupied in investigations relating to the migratory pelagic fishes, giving special attention to the characteristics of mackerel from different localities, some 1500 of these fish having been subjected to detailed examination in the course of this enquiry. The samples of mackerel have been obtained from the south-west of Ireland (through H.M. Inspectors of Irish Fisheries), from the North Sea and from America, in addition to those captured near Plymouth. As the results so far obtained refer only to the autumn fish, it has been thought better to defer their publication until after the coming spring fishery, when further samples from the same localities, as well as from the Mediterranean and from Norway, will be examined.Mr. Garstang has also given much time to working out the results of the drift-bottle experiments, a report of which for the year 1897 will be found at p. 199. These experiments have proved more interesting and successful than we had anticipated when they were undertaken, and we purpose continuing and extending them during the coming year.Mr. Holt's papers in the present number of the Journal represent but a portion of the many observations which he has been able to make during the year on the eggs and larvæ of fishes. He has also given much attention to the question of the distribution of fish at different ages in this neighbourhood.