River Lune juvenile fish stock assessment 2002 (annotated draft copy, Site Reports only)

This draft copy of the River Lune juvenile fish stock assessment from 2000 provides "Site Reports" from different water bodies in the Lune catchment. These Site Reports provide brief information on habitat features, fishery classification and comments on species caught and stocking. This document provides no summary or interpretation of the given data.

River Wyre salmon and sea trout spawning habitat restoration / creation project. Final report April 1995

Adult salmon and sea trout rod catches in the River Wyre have been subject to considerable variability over the years. Annual rod catches ranging from 6 to 401 have been reported since records began in 1905. It has long been suspected that the physical nature of the catchment, combined with anthropogenic influences, has resulted in a deleterious effect on the Wyre fishery. Acidification problems in the head water streams (Marshaw Wyre and Tarnbrook Wyre) have been reported and are thought to threaten salmon juvenile survival. The construction of Abbeystead Reservoir and an increased tendency towards rapidly rising water levels during storms (flashiness) 1 are thought to have a significant impact on spawning gravel quality and quantity, both of which are thought to be deteriorating. As part of an overall desire to maintain and improve the migratory salmonid population in the River Wyre, this project has been commissioned to investigate remedial action which may improve and enhance spawning success, leading to an eventual improvement in the status of adult stocks. The primary objective is to establish whether the quantity and/or quality of available spawning gravels are limiting migratory salmonid productivity. The investigations undertaken confirm the general observation that useable spawning gravels appear to be in short supply in the River Wyre, and may be the limiting factor influencing returning adult stock.

The proposed Lune net limitation order 1999 and associated byelaws

The River Lune rises in the hills around Tebay in thje North of England and runs through rural farming country to Morecambe bay. It is generally considered as a river of high purity and unspoiled nature. The salmon fishery was at one time considered amongst the best in England and Wales, with very high catches to both rod and net fishermen. During the late 1960's the disease UDN decimated the stock. Since then there has been a recovery of the stock, but this is considered by most anglers and netsmen to be a partial recovery of some of the previous stock components. In recent years anglers and netsmen have voiced their concerns over the Lune stock and have lobbied for action to improve the Lune fishery. This net limitation order (NLO) and the separate byelaw in conjunction with habitat improvement are proposed as part of the strategy for future conservation and management of this salmon fishery. The fishery is currently exploited by 37 licensed netsmen, the highest number of any single estuary in England and Wales. There are 26 haaf, 10 drift and 1 seine nets available. Current estimates of the rod fishery are that 1100 to 1400 anglers fish 14 000 days per year. The River Luhe is one of the few rivers within England and Wales that has the benefit of an accurate fish counter. The counter is at Forge Weir approximately 4 km upstream of the tidal limit. The counts, together with records of the catches from the rod and net fishery, enable a reasonably accurate assessment of both rod and net exploitation. Extensive surveys of the juvenile population, carried out in 1991 and 1997, provide additional information. The purpose of this document is to describe and explain the current state of the salmon population in the River Lune and in doing so, demonstrate the current need for stock conservation. A second purpose is to demonstrate that the proposed NLO and byelaw package should allow the salmon population to reach its conservation target (spawning escapement target).

A comparative study of consumption rates and preference for some species of aquatic plants by Tilapia rendalli

The daily consumption rates and preference of juvenile Tilapia rendalli for some macrophytes, Ceratophyllum demersum, Lagarosiphon major, Najas pectinatas and Valisneria aethiopica were determined. Fish were offered single macrophyte diets to determine daily consumption and a mixture of the 4 macrophytes in equal quantities to determine selection. Consumption rates were 821.50 mg, 829.05 mg, 940.00 mg and 2293.53 mg per fish per day, respectively. The differences in consumption rates were significant. Preference was shown for V.aethiopica, whilst C.demersum was least selected. Fish fed on single species lost weight whereas those fed on a variety of macrophytes gained in weight.

River Wyre salmon and sea trout spawning habitat restoration / creation project. Gravel enhancement schemes.

As part of an overall desire to maintain and improve the migratory salmonid population in the River Wyre, a project was commissioned to investigate remedial action which may improve and enhance spawning success and lead to an eventual improvement in the status of adult stocks. The report, titled "River Wyre Salmon and Sea Trout Spawning Habitat Restoration/Creation Project", concluded that usable spawning gravels appeared to be in short supply in the River Wyre catchment and may be the limiting factor influencing the returning adult stock, as juvenile nursery habitat was not found to be limiting. This report looks at gravel enhancement schemes to improve River Wyre salmon and sea trout spawning habitat restoration. It examines methods for gravel enhancement schemes: mechanical cleaning and construction of gravel addition structures. Includes sites figures of sites identified for enhancement.

Gillnet selectivity for juvenile blacktip sharks (Carcharhinus limbatus)

Gillnet mesh selectivity parameters were estimated for juvenile blacktip sharks (Carcharhinus limbatus) by using length data from an experimental fishery-independent gillnet survey in the northeastern Gulf of Mexico. Length data for 1720 blacktip sharks were collected over 17 years (1994–2010) with seven mesh sizes ranging from 7.6 to 20.3 cm. Four selectivity models, a normal model assuming fixed spread, a normal model assuming that spread is proportional to mesh size, a lognormal model, and a gamma model were fitted to the data by using the SELECT (share each length’s catch total) method. Each model was run twice under separate assumptions of 1) equal fishing intensity; and 2) fishing intensity proportional to mesh size. The normal, fixed-spread selectivity curve where fishing intensity is assumed to be proportional to mesh size provided the best fit to the data according to model deviance estimates and was chosen as the best model. Results indicate that juvenile blacktip sharks are susceptible as bycatch in some commercial gillnet fisheries.

Catch rates and demographics of loggerhead sea turtles (Caretta caretta) captured from the Charleston, South Carolina, shipping channel during the period of mandatory use of turtle excluder devices (TEDs)

Trawling was conducted in the Charleston, South Carolina, shipping channel between May and August during 2004–07 to evaluate loggerhead sea turtle (Caretta caretta) catch rates and demographic distributions. Two hundred and twenty individual loggerheads were captured in 432 trawling events during eight sampling periods lasting 2–10 days each. Catch was analyzed by using a generalized linear model. Data were fitted to a negative binomial distribution with the log of standardized sampling effort (i.e., an hour of sampling with a net head rope length standardized to 30.5 m) for each event treated as an offset term. Among 21 variables, factors, and interactions, five terms were significant in the final model, which accounted for 45% of model deviance. Highly significant differences in catch were noted among sampling periods and sampling locations within the channel, with greatest catch furthest seaward consistent with historical observations. Loggerhead sea turtle catch rates in 2004–07 were greater than in 1991–92 when mandatory use of turtle excluder devices was beginning to be phased in. Concurrent with increased catch rates, loggerheads captured in 2004–07 were larger than in 1991–92. Eighty-five percent of loggerheads captured were ≤75.0 cm straight-line carapace length (nuchal notch to tip of carapace) and there was a 3.9:1 female-to-male bias, consistent with limited data for this location two decades earlier. Only juvenile loggerheads ≤75.0 cm possessed haplotypes other than CC-A01 or CC-A02 that dominate in the region. Six rare and one un-described haplotype were predominantly found in June 2004.

Life-stage recruitment models for Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on Georges Bank

Ichthyoplankton surveys have been used to provide an independent estimate of adult spawning biomass of commercially exploited species and to further our understanding of the recruitment processes in the early life stages. However, predicting recruitment has been difficult because of the complex interaction of physical and biological processes operating at different spatial and temporal scales that can occur at the different life stages. A model of first-year life-stage recruitment was applied to Georges Bank Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) stocks over the years 1977–2004 by using environmental and densitydependent relationships. The best lifestage mortality relationships for eggs, larvae, pelagic juveniles, and demersal juveniles were first determined by hindcasting recruitment estimates based on egg and larval abundance and mortality rates derived from two intensive sampling periods, 1977–87 and 1995–99. A wind-driven egg mortality relationship was used to estimate losses due to transport off the bank, and a wind-stress larval mortality relationship was derived from feeding and survival studies. A simple metric for the density-dependent effects of Atlantic cod was used for both Atlantic cod and haddock. These life stage proxies were then applied to the virtual population analysis (VPA) derived annual egg abundances to predict age-1 recruitment. Best models were determined from the correlation of predicted and VPA-derived age-1 abundance. The larval stage was the most quantifiable of any stage from surveys, whereas abundance estimates of the demersal juvenile stage were not available because of undersampling. Attempts to forecast recruitment from spawning stock biomass or egg abundance, however, will always be poor because of variable egg survival.

Regional variation in the annual feeding cycle of juvenile walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska

Juvenile fish in temperate coastal oceans exhibit an annual cycle of feeding, and within this cycle, poor wintertime feeding can reduce body growth, condition, and perhaps survival, especially in food-poor areas. We examined the stomach contents of juvenile walleye pollock (Theragra chalcogramma) to explain previously observed seasonal and regional variation in juvenile body condition. Juvenile walleye pollock (1732 fish, 37–250 mm standard length) of the 2000 year class were collected from three regions in the Gulf of Alaska (Kodiak, Semidi, and Shumagin) representing an area of the continental shelf of ca. 100,000 km2 during four seasons (August 2000 to September 2001). Mean stomach content weight (SCW, 0.72% somatic body weight) decreased with fish body length except from winter to summer 2001. Euphausiids composed 61% of SCW and were the main determinant of seasonal change in the diets of fish in the Kodiak and Semidi regions. Before and during winter, SCW and the euphausiid dietary component were highest in the Kodiak region. Bioenergetics modeling indicated a relatively high growth rate for Kodiak juveniles during winter (0.33 mm standard length/d). After winter, Shumagin juveniles had relatively high SCW and, unlike the Kodiak and Semidi juveniles, exhibited no reduction in the euphausiid dietary component. These patterns explain previous seasonal and regional differences in body condition. We hypothesize that high-quality feeding locations (and perhaps nursery areas) shift seasonally in response to the availability of euphausiid

Interactions of age-dependent mortality and selectivity functions in age-based stock assessment models

The natural mortality rate (M) of fish varies with size and age, although it is often assumed to be constant in stock assessments. Misspecification of M may bias important assessment quantities. We simulated fishery data, using an age-based population model, and then conducted stock assessments on the simulated data. Results were compared to known values. Misspecification of M had a negligible effect on the estimation of relative stock depletion; however, misspecification of M had a large effect on the estimation of parameters describing the stock recruitment relationship, age-specific selectivity, and catchability. If high M occurs in juvenile and old fish, but is misspecified in the assessment model, virgin biomass and catchability are often poorly estimated. In addition, stock recruitment relationships are often very difficult to estimate, and steepness values are commonly estimated at the upper bound (1.0) and overfishing limits tend to be biased low. Natural mortality can be estimated in assessment models if M is constant across ages or if selectivity is asymptotic. However if M is higher in old fish and selectivity is dome-shaped, M and the selectivity cannot both be adequately estimated because of strong interactions between M and selectivity.

Age validation, growth, mortality, and demographic modeling of spotted gully shark (Triakis megalopterus) from the southeast coast of South Africa

This study documents validation of vertebral band-pair formation in spotted gully shark (Triakis megalopterus) with the use of fluorochrome injection and tagging of captive and wild sharks over a 21-year period. Growth and mortality rates of T. megalopterus were also estimated and a demographic analysis of the species was conducted. Of the 23 OTC (oxytetracycline) -marked vertebrae examined (12 from captive and 11 from wild sharks), seven vertebrae (three from captive and four from wild sharks) exhibited chelation of the OTC and fluoresced under ultraviolet light. It was concluded that a single opaque and translucent band pair was deposited annually up to at least 25 years of age, the maximum age recorded. Reader precision was assessed by using an index of average percent error calculated at 5%. No significant differences were found between male and female growth patterns (P>0.05), and von Bertalanffy growth model parameters for combined sexes were estimated to be L∞=1711.07 mm TL, k=0.11/yr and t0=–2.43 yr (n=86). Natural mortality was estimated at 0.17/yr. Age at maturity was estimated at 11 years for males and 15 years for females. Results of the demographic analysis showed that the population, in the absence of fishing mortality, was stable and not significantly different from zero and particularly sensitive to overfishing. At the current age at first capture and natural mortality rate, the fishing mortality rate required to result in negative population growth was low at F>0.004/ yr. Elasticity analysis revealed that juvenile survival was the principal factor in explaining variability in population growth rate.

Spatial and temporal variation in otolith chemistry for tautog (Tautoga onitis) in Narragansett Bay and Rhode Island coastal ponds

The elemental composition of otoliths may provide valuable information for establishing connectivity between fish nursery grounds and adult fish populations. Concentrations of Rb, Mg, Ca, Mn, Sr, Na, K, Sr, Pb, and Ba were determined by using solution-based inductively coupled plasma mass spectrometry in otoliths of young-of-the year tautog (Tautoga onitis) captured in nursery areas along the Rhode Island coast during two consecutive years. Stable oxygen (δ18O) and carbon (δ13C) isotopic ratios in young-of-the year otoliths were also analyzed with isotope ratio mass spectrometry. Chemical signatures differed significantly among the distinct nurseries within Narragansett Bay and the coastal ponds across years. Significant differences were also observed within nurseries from year to year. Classification accuracy to each of the five tautog nursery areas ranged from 85% to 92% across years. Because accurate classification of juvenile tautog nursery sites was achieved, otolith chemistry can potentially be used as a natural habitat tag.

Seasonal variability in ichthyoplankton abundance and assemblage composition in the northern Gulf of Mexico off Alabama

Multiyear ichthyoplankton surveys used to monitor larval fish seasonality, abundance, and assemblage structure can provide early indicators of regional ecosystem changes. Numerous ichthyoplankton surveys have been conducted in the northern Gulf of Mexico, but few have had high levels of temporal resolution and sample replication. In this study, ichthyoplankton samples were collected monthly (October 2004–October 2006) at a single station off the coast of Alabama as part of a long-term biological survey. Four seasonal periods were identified from observed and historic water temperatures, including a relatively long (June–October) “summer” period (water temperature >26°C). Fish egg abundance, total larval abundance, and larval taxonomic diversity were significantly related to water temperature (but not salinity), with peaks in the spring, spring–summer, and summer periods, respectively. Larvae collected during the survey represented 58 different families, of which engraulids, sciaenids, carangids, and clupeids were the most prominent. The most abundant taxa collected were unidentified engraulids (50%), sand seatrout (Cynoscion arenarius, 7.5%), Atlantic bumper (Chloroscombrus chrysurus, 5.4%), Atlantic croaker (Micropogonias undulatus, 4.4%), Gulf menhaden (Brevoortia patronus, 3.8%), and unidentified gobiids (3.6%). Larval concentrations for dominant taxa were highly variable between years, but the timing of seasonal occurrence for these taxa was relatively consistent. Documented increases in sea surface temperature on the Alabama shelf may have various implications for larval fish dynamics, as indicated by the presence of tropical larval forms (e.g., fistularids, labrids, scarids, and acanthurids) in our ichthyoplankton collections and in recent juvenile surveys of Alabama and northern Gulf of Mexico seagrass habitats.

Effects of starvation on energy density of juvenile chum salmon (Oncorhynchus keta) captured in marine waters of Southeastern Alaska

We conducted laboratory starvation experiments on juvenile chum salmon (Oncorhynchus keta) captured in the neritic marine waters of northern Southeast Alaska in June and July 2003. Temporal changes in fish energy density (whole body energy content [WBEC], cal/g dry weight), percent moisture content, wet weight (g), length (mm), and size-related condition residuals were measured in the laboratory and were then compared to long-term field data. Laboratory water temperatures and salinities averaged 9°C and 32 psu in both months. Trends in response variables were similar for both experimental groups, although sampling intervals were limited in July because fewer fish were available (n= 54) than in June (n=101). Overall, for June (45-d experimental period, 9 intervals), WBEC, wet weight, and condition residuals decreased and percent moisture content increased, whereas fork length did not change. For July (20-d experimental period, 5 intervals), WBEC and condition residuals decreased, percent moisture content and fork length increased, and wet weight did not change. WBEC, percent moisture content, and condition residuals fell outside the norm of longterm data ranges within 10–15 days of starvation, and may be more useful than fork length and wet weight for detecting fish condition responses to suboptimal environments.

Larval development of the spotfin tonguefish (Symphurus oligomerus Mahadeva and Munroe, 1990) (Pleuronectiformes: Cynoglossidae) from the Gulf of California, Mexico

Larval and early juvenile stages of Symphurus oligomerus are described from 24 specimens from the Gulf of California. Meristic features were 48 – 49 total vertebrae, 87–94 dorsal-fin rays, 73–77 anal-fin rays, 12 caudal-fin rays, and five hypural bones. Seven larvae and one juvenile were cleared and stained to obtain the pterygiophore formula (1-3-2-2-2) that confirmed the identification of S. oligomerus. The pigment pattern from preflexion to juvenile stage consists of three bands on the dorsal margin and two bands on the ventral margin formed by star-shaped melanophores on the left side of the body. The intestine in preflexion to postflexion larvae forms an abdominal projection that ends in a short conical appendix. The intestine is supported by three cartilaginous struts; larvae with these physical attributes are called exterilium larvae. Preflexion larvae have two elongated dorsal-fin rays, and in flexion to postflexion larvae the second to the fourth dorsalfin rays are elongate. We found an apparent connection between the size at metamorphosis of the species of Symphurus and the depth distribution range of adults such that the fish species that metamorphose at a larger size have a deeper distribution as adults and exterilium larvae seem to correspond to species that have deeper distributions.