Environmental effects on the spatio‐temporal patterns of abundance and distribution of Sardina pilchardus and sardinella off the Mauritanian coast (North‐West Africa)

From 1998 to 2011, the effects of environmental conditions on the spatial and temporal trends of sardine and sardinella catch rates in the Mauritanian waters were investigated using generalized additive models. Two models were used: a global model and an oceanographic model. The global models explained more of the variability in catch rates (60.4% for sardine and 40% for sardinella) than the oceanographic models (42% for sardine and 32.4% for sardinella). Both species showed clear and inverse seasonal variations in abundances corresponding to their main spawning activities and the hydrologic seasons off the Mauritanian waters. Sardine prefer colder waters and seem to occupy the ‘gap’ in the northern part of the Mauritanian waters as soon as sardinella has left the area because of to lower water temperatures. Unlike sardinella, sardine showed a gradual southward extension between 2002 and 2009. The oceanographic model revealed that a high proportion of catch variability for the two species could be explained by environmental variables. The main environmental parameters explaining the variability are sea surface temperature (SST) and the upwelling index for sardinella, and the chlorophyll‐a (Chl‐a) concentration, the upwelling index and SST for sardine. The sardinella spatio‐temporal variations off Mauritania seem to be more controlled by thermal than productivity gradients, probably linked to the species physiological constraints (thermal tolerance) whereas sardine seems to be more controlled by an ‘optimal upwelling and temperature’ windows. The results presented herein may be useful for understanding the movement of these species along the Mauritanian coast and hence their management under a changing climate.     

Changes in the spawning habitat of two small pelagic fish in the Northwestern Mediterranean

We investigated the effects of three sea surface oceanographic variables (temperature, salinity, and chlorophyll a) on the abundance of eggs and larvae of two summer‐spawning species in the NW Mediterranean Sea, the anchovy Engraulis encrasicolus and the round sardinella Sardinella aurita, based on data from ichthyoplankton surveys carried out in the 1980s, 2000s, and 2010s. The environmental data showed an increase in seawater temperature and salinity along time, coupled with a decrease in chlorophyll a (proxy for primary production). These long‐term directional changes in environmental conditions helped explain the important reduction observed in the abundance of eggs and larvae of anchovy, as well as shrinking of spawning habitat in this species. At the same time, the probability of occurrence of round sardinella has increased from practically zero in the 1980s to probabilities near 1 along the coastal area of the study region in the two decades of the 21st century. Given that the trends observed in the environmental variables along the three decades of study are expected to continue during the 21st century, as a consequence of climate change, the spawning habitat of anchovy is expected to continue decreasing, while round sardinella habitat can expand. Considering that anchovy is of high commercial importance in NW Mediterranean fisheries, while round sardinella has very low commercial interest, our results show that the viability of small pelagic fisheries in the area may be compromised.     

The impact of methodological choices on the outcome of national‐level climate change vulnerability assessments: An example from the global fisheries sector

Climate change vulnerability assessments have been receiving increasing attention from policymakers and academics. Given scarce funds for adaptation, the UNFCCC Secretariat has suggested that eligible countries be prioritized for support based on their vulnerability to climate change. National‐level fisheries sector climate change vulnerability assessments as well as other overall vulnerability assessments to date have lent support to the idea that least developed countries (LDCs) are more vulnerable to climate change than small island developing states (SIDS) and other coastal countries. We demonstrate that these perceived differences in vulnerability among country groups are partly due to methodological choices made during these assessments. We argue that national‐level vulnerability assessments, and particularly those dealing with the fisheries sector, often suffer from four main methodological shortcomings: (i) an inconsistent representation of countries belonging to each group, (ii) use of socioeconomic indicators that are not scaled to population size, (iii) use of a small number of indicators and (iv) lack of accounting for potential redundancy among indicators. Building on a previous framework, we show that by addressing the four aforementioned methodological shortcomings, the ranking in fisheries sector vulnerability among SIDS, LDCs and other coastal countries is altered significantly. Our results underscore that the vulnerability of SIDS was partially concealed in previous assessments and suggest that SIDS are in fact the most vulnerable group. Although this study focuses on assessing the vulnerability of the fisheries sector to climate change in SIDS, LDCs and other coastal countries, the implications also apply to other sectors and country groupings.     

Reconstructing 290 years of a data‐poor fishery through ethnographic and archival research: The East Pacific green turtle (Chelonia mydas) in Baja California,Mexico

Evaluating historical changes in the exploitation of marine organisms is a key challenge in fisheries ecology and marine conservation. In the Eastern Pacific, marine turtles were exploited for millennia before systematic monitoring began <50 years ago. Using ethnographic and historical data, we generated a detailed reconstruction of the East Pacific green sea turtle (Chelonia mydas) fishery in Mexico's Baja California peninsula from 1700 to 1990. Sea turtles from the region's important feeding areas were a staple food source from the earliest phases of human occupation, dating back at least 12,000 years. In contrast with regions such as the Caribbean, small human populations and limited market access resulted in apparently sustainable turtle harvests until the second half of the 20th century. We found that the estimated annual catches between 1960 and 1980 exceeded the estimated annual catches of the previous 250 years by an order of magnitude, leading to the collapse of the fishery and the depletion of the green turtle population. A total ban on sea turtle captures in 1990, comprehensive nesting beach protection, and significant conservation efforts resulted in increases in breeding females on nesting beaches and catch rates in scientific monitoring on main feeding grounds since the early 2000s. This provides a positive outlook for this once‐depleted population segment. Although further research is needed to evaluate current conservation status, we have identified a date, between 1950 and 1960, which can serve as a reliable temporal reference for future evaluations of historical baseline abundance in this region.     

Modelling transport of inshore and deep‐spawned chokka squid (Loligo reynaudi) paralarvae off South Africa: the potential contribution of deep spawning to recruitment

The South African chokka squid, Loligo reynaudi, spawns both inshore (≤70 m) and on the mid‐shelf (71–130 m) of the Eastern Agulhas Bank. The fate of these deep‐spawned hatchlings and their potential contribution to recruitment is as yet unknown. Lagrangian ROMS‐IBM (Regional Ocean Modelling System‐Individual‐Based Model) simulations confirm westward transport of inshore and deep‐spawned hatchlings, but also indicate that the potential exists for paralarvae hatched on the Eastern Agulhas Bank deep spawning grounds to be removed from the shelf ecosystem. Using a ROMS‐IBM, this study determined the transport and recruitment success of deep‐spawned hatchlings relative to inshore‐hatched paralarvae. A total of 12 release sites were incorporated into the model, six inshore and six deep‐spawning sites. Paralarval survival was estimated based on timely transport to nursery grounds, adequate retention within the nursery grounds and retention on the Agulhas Bank shelf (<200 m). Paralarval transport and survival were dependent on both spawning location and time of hatching. Results suggest the importance of the south coast as a nursery area for inshore‐hatched paralarvae, and similarly the cold ridge nursery grounds for deep‐hatched paralarvae. Possible relationships between periods of highest recruitment success and spawning peaks were identified for both spawning habitats. Based on the likely autumn increase in deep spawning off the Tsitsikamma coast, and the beneficial currents during this period (as indicated by the model results) it can be concluded that deep spawning may at times contribute significantly to recruitment.     

The use of at‐sea‐sampling data to dissociate environmental variability in Norway lobster (Nephrops norvegicus) catches to improve resource exploitation efficiency within the Skagerrak/Kattegat trawl fishery

Research into the influence of environmental variables on the behaviour of Norway lobster (Nephrops norvegicus), and hence catch rates, dates back to the 1960s (e.g., Höglund and Dybern, Diurnal and seasonal variations in the catch‐composition of Nephrops norvegicus (L.) at the Swedish west coast. ICES CM 1965/I46; Simpson, Variations in the catches of Nephrops norvegicus at different times of day and night. Rapport et Proés‐verbaux des Réunions Conseil permanent international pour 1'Exploration de la Mer 156:186). However, the use of fishery‐dependent data in identifying influential factors is relatively limited and only includes a number of papers on a limited dataset (e.g., Redant and De Clark, Diurnal variations in CPUE and length composition of the catches in a Nephrops directed fishery in the Central North Sea. ICES CM 1984/K:3; Maynou and Sardà, Influence of environmental factors on commercial trawl catches of Nephrops norvegicus (L.). ICES J. Mar. Sci. 58:1318). Here, we aimed to dissociate environmental variability in Norway lobster catches to improve resource exploitation efficiency within the Skagerrak and Kattegat trawl fisheries by utilising data collected as part of an extensive at‐sea‐sampling programme spanning 16 years. Catch rates were modelled using Generalized Additive Mixed Models (GAMMs) and considered a range of response variables, including depth, temperature, current speed, season, moon phase and time of day. The results obtained herein showed that time of day, season, depth, temperature, year, trawl type and location all significantly affect catch rates of Nephrops.     

Effect of size‐fractionated fish protein hydrolysate on growth and feed utilization of turbot (Scophthalmus maximus L.)

Four experimental diets were fed to turbot to examine the effect of fish hydrolysate and ultra‐filtered fish hydrolysate on growth performance, feed utilization and non‐specific immune response. Fish hydrolysate was produced by enzymatic treatment and size fractionated using ultra‐filtration (UF). The permeate (molecular weight <1000 Da) after UF and the non‐ultra‐filtered fish hydrolysate (NUF) were tested as feed ingredients. Diets UF1, UF2 contained 3.7%, 1.2% ultra‐filtered fish hydrolysate to replace fish meal protein respectively. The diets UF1, NUF were identical in composition except that the molecular weight of fish hydrolysate in the diet. Fish meal was used in the control diet. All diets were made equal in protein, lipid and energy. Each experimental diet was fed to juvenile turbot (27.87 ± 0.04 g) in triplicate for 8 weeks. Results of this study indicate that the best overall growth and feed utilization of turbot juveniles were obtained with a diet containing higher dose of the small molecular weight compounds in fish hydrolysate. Acid phosphatase, alkaline phosphatase, lysozyme and superoxide dismutase activity in serum were not affected by diet. Total antioxidant capacity was improved with increasing level of low molecule weight fish hydrolysate (UF1).     

Immune responses of Litopenaeus vannamei to non‐ionic ammonia stress: a comparative study on shrimps in freshwater and seawater conditions

To investigate the effect of non‐ionic ammonia (NH₃‐N) stress (0.1 and 0.5 mg L^?1) on the immunity of Litopenaeus vannamei cultured in long‐term freshwater, the total haemocyte count (THC), the activity of phenoloxidase (PO), nitric oxide synthase (NOS), superoxidase dismutase (SOD) and the content of malondialdehyde (MDA) were determined and further compared with those of seawater shrimps. The results showed that NH₃‐N stress significantly reduced THC and the activity of PO and SOD (P < 0.05). Under 0.1 mg L^?1 NH₃‐N stress, NOS activity increased first and then decreased significantly, while it dropped dramatically under 0.5 mg L^?1 NH₃‐N stress (P < 0.05). During NH₃‐N stress, MDA content increased continuously, and the MDA content in hepatopancreas of freshwater shrimps was higher than that of seawater shrimps. It was concluded that NH₃‐N stress significantly influenced the non‐specific immunity and could also upset the balance of antioxidant system of L. vannamei in both freshwater and seawater shrimps. Compared with in seawater, the shrimps in freshwater were more vulnerable to NH₃‐N stress because of higher lipid peroxidation and lower immunity.     

The effect of lake morphometry on thermal habitat use and growth in Arctic charr populations: implications for understanding climate‐change impacts

Oxygen stable isotope temperature reconstruction methods were used to estimate mean experienced summer temperatures from growth zones within individual Arctic charr otoliths sampled from lakes with contrasting morphologies but proximate locations. For either lake, otolith‐estimated temperatures were not significantly related to back‐calculated growth. Fish in the smaller lake evidenced an increase in growth with age related to increasing use of cooler thermal habitats, with the use of thermal habitat possibly governed by predation risks. No relationships between age, growth or temperature were observed in the larger lake. Significant negative effects on back‐calculated growth were observed due to increasing air temperatures in the smaller and shallower lake, possibly owing to warmer surface and littoral waters and a limited amount of preferred cool‐water habitat. A similar relationship was not observed in the larger and deeper lake and indicated that resident Arctic charr were not as vulnerable to the impacts of temperature warming, possibly because of better behavioural thermoregulation opportunities in the cooler, deeper lake. Results provide evidence for differing climate‐influenced growth outcomes among proximately located populations, with outcomes likely to depend on the differences among habitats, including lake size and morphometry which may act to influence fish densities in available preferred thermal habitats.     

Optimization of de‐oiled rice bran inclusion level in the diet of Labeo rohita: Effect on growth performance,nutrient utilization,insulin‐like growth factors I and II gene expression

A 60‐day feeding trial was conducted to optimize the inclusion level of de‐oiled rice bran (DORB) in the diet of Labeo rohita fingerlings. Six iso‐nitrogenous (260g/kg), iso‐lipidic (70g/kg) and iso‐energetic (15 MJ/Kg) diets were prepared with different inclusion level of DORB viz., T33, T38_, T43, T48, T53 and T58. One hundred and eighty fingerlings (9.8 ± 0.5 g) were randomly distributed in seven experimental groups in triplicates following a completely randomized design. The weight gain %, specific growth rate, protein efficiency ratio and feed efficiency ratio were found similar in 33%, 38% and 43% DORB fed groups. The expression of both insulin‐like growth factors I and II (IGF‐I and II) was significantly (p < 0.05) higher in T33, T38 and T43 groups. Based on second order polynomial regression analysis (y = ?0.0059x² + 0.4573x ? 4.8404, R² = 0.95), the expression of IGF‐I was found to be maximum at 39.5% inclusion level of DORB. Significantly (p < 0.05) lower muscle RNA content, RNA‐DNA ratio and higher feed conversion ratio were found in T58 group. Hence, from these results, it can be concluded that the optimum inclusion of DORB in the diet (260g/kg CP and 70g/kg lipid) of L. rohita should be 39.5% to support maximum nutrient utilization and growth performance.     

Effect of aromatable androgen (17‐methyltestosterone) on induced maturation of silver European eels (Anguilla Anguilla): Oocyte performance and synchronization

The reproductive performances of silver European eel in term of gonad development and egg production, employing slow‐release implants with the androgen 17‐MT (1 mg) in combination with traditional weekly injection of carp pituitary extract (CPE) was evaluated. Wild female European eels (Anguilla anguilla) underwent a standard induction protocol with CPE and were randomly divided into three groups (N‐group, no implant; Y‐group, with implant; and control, C‐group, no treatment). The results showed that 17‐MT‐treated females (Y‐group) reproduced spontaneously about 6 weeks earlier than the N‐group females with a saving of almost 40% in CPE and time of induction. Concerning artificial induction of maturation in female silver eels, our study demonstrated that they positively respond to androgen exposure also in terms of eggs productivity. Indeed, Y‐group was more productive than N‐group: in Y‐group, 11 eels ensured an eggs production that exceeded 50% of initial body weight (BW), whereas in N‐group only three eels have exceeded this value. The results suggest that 17‐MT should be considered in future protocols for the improvement of the artificial reproduction of female silver European eels.