Diversity and distribution of early life stages of carangid fishes in the northwestern Mediterranean: responses to environmental drivers

The diversity and distribution of the early stages of carangid fishes were investigated in relation to environmental conditions off the Catalan Coast (NW Mediterranean). Data were obtained during four oceanographic cruises conducted in spring–summer 2003 and 2004. A total of 4743 larvae from seven species and five genera were identified. Most were thermophilic species very abundant in the warm waters of the south and eastern Mediterranean. The presence of larvae and juveniles of Caranx crysos, Caranx rhonchus, Seriola dumerili and Trachinotus ovatus in the northwestern Mediterranean is reported for the first time. Except for Trachurus trachurus, which spawns in winter–spring, all species reproduce in spring–summer with a temporal succession in their spawning peaks. On average, the spatial patterns of different species (except T. trachurus) showed common features: a clear preference for spawning in coastal areas, high abundance of larvae in the south warmer zone in relation to the surface productive waters of Ebro river runoff and relatively high larval concentrations south of the thermal front and its associated anticyclonic eddy. The presence of larvae of thermophilic species of carangids in the northwestern Mediterranean indicates successful reproduction and establishment of these species in the cold part of the basin.     

Habitat differentiation between sei (Balaenoptera borealis) and Bryde's whales (B. brydei) in the western North Pacific

Two closely related baleen whale species, sei and Bryde's whales, in the western North Pacific were studied to identify differences in habitat use. Data were obtained from May to August 2004 and 2005. This study examined the relationship between oceanographic features derived from satellite data and the distribution of sei and Bryde's whales using basic statistics. We investigated oceanographic features including sea surface temperature (SST), sea surface chlorophyll a (Chl‐a), sea surface height anomalies (SSHAs), and depth of the habitat. These two whale species used habitats with different SST, Chl‐a, and SSHA ranges. The 0.25 mg m^?3 Chl‐a contour (similar to the definition of the Transition Zone Chlorophyll Front) was a good indicator that separated the habitats of sei and Bryde's whales. Then generalized linear models were used to model the probabilities that the whale species would be present in a habitat and to estimate their habitat distribution throughout the study area as a function of environmental variables. The potential habitats of the two species were clearly divided, and the boundary moved north with seasonal progression. The habitat partitioning results indicated that SST contributed to the patterns of habitat‐use and might reflect differences in prey species between the two whales. This study showed that the habitats of the sei and Bryde's whales were clearly divided and their potential habitat‐use changed seasonally.     

Oceanographic factors affecting interannual recruitment variability of Pacific saury (Cololabis saira) in the central and western North Pacific

Pacific saury (Cololabis saira) has a short life span of 2 years and tends to exhibit marked population fluctuations. To examine the importance of sea surface temperature (SST) and mixed layer depth (MLD) as oceanographic factors for interannual variability of saury recruitment in early life history, we analyzed the relationship between abundance index (survey CPUE (catch per unit of effort)) of age‐1 fish and the oceanographic factors in the spawning and nursery grounds of the previous year when they were born, for the period of 1979–2006, in the central and western North Pacific. Applying the mixture of two linear regression models, the variability in the survey CPUE was positively correlated with previous year's winter SST in the Kuroshio Recirculation region (KR) throughout the survey period except 1994–2002. In contrast, the survey CPUE was positively correlated with the previous year's spring MLD (a proxy of spring chlorophyll a (Chl‐a) concentration) in the Kuroshio‐Oyashio Transition and Kuroshio Extension (TKE) during 1994–2002. This period is characterized by unusually deep spring MLD during 1994–1997 and anomalous climate conditions during 1998–2002. We suggest that saury recruitment variability was generally driven by the winter SST in the KR (winter spawning/nursery ground), or by the spring Chl‐a concentration (a proxy of prey for saury larvae) in the TKE (spring spawning/nursery ground). These oceanographic factors could be potentially useful to predict abundance trends of age‐1 saury in the future if the conditions leading to the switch between SST and MLD as the key input variable are elucidated further.     

Operational oceanography applied to skipjack tuna (Katsuwonus pelamis) habitat monitoring and fishing in south‐western Atlantic

Skipjack tuna (Katsuwonus pelamis) ranks third among marine resources that sustain global fisheries. This study delimits the spatiotemporal habitat of the species in the south‐western Atlantic Ocean, based on operational oceanography. We used generalized additive models (GAMs) and catch data from six pole‐and‐line fishing vessels operating during 2014 and 2015 fishing seasons to assess the effect of environmental variables on catch. We also analysed Modis sensor images of sea surface temperature (SST) and surface chlorophyll‐α concentration (SCC) to describe fishing ground characteristics in time and space. Catch was positively related to thermocline depth (24–45 m), SST (22–24.5°C), SCC (0.08–0.14 mg/m³) and salinity (34.9–35.8). Through SST images, we identified that thermal fronts were the main surface feature associated with a higher probability to find skipjack. Also, we state that skipjack fishery is tightly related to shelf break because bottom topography drives the position of fronts in this area. Ocean colour fronts and plankton enrichment were important proxies, accessible through SCC, used to delineate skipjack fishing grounds. Catch per unit effort (CPUE) was higher towards summer (median 14 t/fishing day) due to the oceanographic characteristics of the southern region. High productivity in this sector of the Brazilian coast defines the main skipjack feeding areas and, as a consequence, the greatest abundance and availability for fishing.     

El Niño–Southern Oscillation impacts on jumbo squid habitat: Implication for fisheries management

1. Dosidicus gigas is an ecologically and economically important squid species extensively distributed in the eastern Pacific Ocean. Its habitat is extremely sensitive to climatic and environmental variability.
2. The relationship between habitat pattern of D. gigas and El Niño–Southern Oscillation (ENSO, divided into the El Niño, ENSO-neutral, and La Niña events) was assessed from 1950 to 2015, using a habitat suitability index (HSI) modelling approach including two crucial environmental variables: sea surface temperature (SST) and sea surface height anomaly (SSHA).
3. On the basis of cross-correlation analysis, it showed that both SST anomaly and SSHA were significantly positively related to the ENSO index. Moreover, a significantly negative association was found between the HSI values and the ENSO index.
4. Due to the El Niño events, SST off Peru became higher and sea level rose, resulting in contracted areas of suitable SST and SSHA; consequently, suitable habitats for D. gigas dramatically decreased. In contrast, during the ENSO-neutral and La Niña years, the extent of suitable SST and SSHA increased due to the colder water and lower sea level, and suitable habitat for D. gigas expanded.
5. Moreover, the latitudinal gravity centre of HSI was significantly positively associated with the ENSO index. Relative to the ENSO-neutral and La Niña years, a southward movement of the monthly preferred SST isotherm for D. gigas during the El Niño years could explain the occurrence of more suitable habitats in southern waters off Peru.
6. These findings suggested that the ENSO event plays an important role in regulating environmental conditions off Peru and further affected the spatio-temporal distribution of D. gigas habitat.

     

Subtropical water influences temporal fluctuations of early life stages of Vinciguerria lucetia (Osteichthyes: Phosichthyidae) in the Humboldt Current System (1998–2004)

In the last decades, the fish Vinciguerria lucetia (Garman) has been of important interest to the fisheries sector; nonetheless, the spawning and nursery zones in the Humboldt Current System (HCS) have not yet been defined. By using a temporal series of 23 oceanographic surveys from austral spring of 1998 to autumn 2004 off northern Chile, the spatial and temporal distribution and abundance of eggs and larvae of V. lucetia were studied. The relationships with environmental conditions (sea surface temperature, water column stratification, salinity, dissolved oxygen) were modeled using generalized additive models (GAMs). Seasonal variations in eggs and larval abundances were recorded, and higher abundances were observed in spring and summer, respectively. The main spawning areas were located at approximately between 40 and 80 nautical miles offshore. The largest abundances of V. lucetia eggs were found during spring 2003; however, larval abundances reached the highest values following the strongest ENSO event 1997–98. GAMs predicted that offshore location, sea surface temperature, and the deepening of the oxygen minimum zone, characteristics of the subtropical waters (22–24°C, >34.9, 3–6 ml/L) drove eggs and larval distributions of V. lucetia in the HCS during 1998–2004, toward areas with scarce food availability for larvae. These results suggest that spawning and larval development of this oceanic species occur in oligotrophic waters as a loophole strategy, in order to reduce predation risk during early life stages.     

Intra‐annual patterns of coastal larval fish assemblages along environmental gradients in the northeastern Mediterranean

To date, little is known about the larval‐fish assemblages (LFAs) in the eastern Mediterranean. The purpose of this study is to investigate the intra‐annual variations of LFAs with an emphasis on the effects of physical, chemical, biological and meteorological conditions in the gulf of Iskenderun, which is a shallow (100 m maximum depth), semi‐enclosed bay located in the northeastern corner of the Mediterranean. The gulf is under the influence of offshore waters throughout the year. The study was based on an ichthyoplankton survey program performed at 28 stations over 12 months, between November 2009 and October 2010. During the study, a total of 11,411 larval individuals belonging to 177 taxa were sampled. The jackknife estimate of maximum species richness was 225 ± 19 for the study area. The maximum larval richness (84 species) and abundance (827 larvae/10 m²) values coincided with spring bloom in April. Gobiids dominated the ichthyoplankton of Iskenderun Bay by constituting 9% of species richness and 42% of total individuals. Four LFAs were identified which were in early winter (November to January), late winter (February and March), spring (April to June) and summer (July to October). The intra‐annual variations of richness, abundance and composition of ichthyoplankton were significantly correlated with the temperature and mesozooplankton biomass. The wind conditions and thermal stratification were also significantly correlated with the composition of LFAs. In conclusion, phenology of LFAs were formed under the influence of physical and tropho‐dynamic conditions in Iskenderun Bay, Northeastern Mediterranean.     

Annual variation in otolith increment widths of walleye pollock (Gadus chalcogrammus) larvae in Funka Bay,Hokkaido, Japan

To clarify relationships between year‐class strength and larval growth of walleye pollock (Gadus chalcogrammus), and oceanographic conditions in the Pacific stock off Hokkaido and Tohoku, Japan, we undertook conductivity/temperature/depth (CTD) observations and investigated larval densities, larval otolith increment widths and larval prey densities (of copepod nauplii) of the 2008, 2009, 2010 and 2011 yr classes in Funka Bay. Oyashio Coastal Water (OCW) flowed into the bay in late February in 2008, 2010 and 2011, and the mean water temperatures decreased to 1.9–3.1 °C in March. OCW was not observed in 2009, and it was warm in late February (≥3.4 °C). Increment widths of lapillar otoliths during the yolk‐sac stage were wide in 2009 and 2011, medium in 2010 and narrow in 2008. Increment widths during the first‐feeding stage tended to become wider as the hatch month progressed, and the annual variation during the first‐feeding stage was larger than that of the yolk‐sac stage. The densities of the primary food for the larvae were high in 2008 when larval increment widths were narrowest, so the effect of prey abundance on larval growth appeared to be small. The ranking of the larval abundance in March was nearly coincident with that of the increment width during the larval stage. We, therefore, suggest that the larval growth rate is associated with the mortality rate and that the growth–mortality hypothesis may be applicable to walleye pollock in Funka Bay. Feeding success under warm water conditions may be an important factor that contributes towards high growth rates.     

A biophysical model to assess the trade‐off between larval recruitment and catch in southern Australia's largest prawn fishery

Data from stock assessment surveys, published research and climate sensors were linked to model the interaction between fishing, physical‐oceanographic processes and spatial patterns of larval settlement for western king prawn [Penaeus (Melicertus) latisulcatus]. This information was used to evaluate the trade‐off between larval recruitment and catch during fishing periods that demand high prices but coincide with spawning. Total rates of larval settlement were maximized when tidal currents and atmospheric physical‐forcing components were coupled with simulations of larval swimming behaviour under average gulf temperatures. Average gulf temperatures sustained longer larval durations and increased larval settlement rates by over 12% compared with warmer gulf conditions simulated under a scenario of global warming. Reproductive data coupled with outputs from the biophysical model identified consistent inter‐annual patterns in the areas contributing to larval settlement success. Areas located in the north‐east, and central‐west of the fishery, consistently contributed to over 40% of all larvae reaching a settlement in each year. Harvest sensitivity analyses indicated that changes in the spatial patterns of pre‐Christmas fishing could lead to improvements in overall rates of the larval settlement while maintaining or improving the levels of catch. Future studies to refine the model inputs relating to physical processes, larval behaviour and mortality rates for P. latisulcatus coupled with surveys of juvenile prawn abundance to ground truth the modelled predictions, would allow stock recruitment relationships to be more closely examined and inform adaptive management of the fishery in the future.     

Assessment of temperature or salinity effects on larval development by catecholamine‐induced metamorphosis of hatchery‐reared flat oyster,Ostrea angasi (Sowerby 1871) larvae

A need to improve larval rearing techniques led to the development of protocols for catecholamine‐induced settlement of flat oyster, Ostrea angasi, larvae. To further refine these techniques and optimize settlement percentages, the influence of salinity or temperature on development of O. angasi larvae was assessed using epinephrine‐induced metamorphosis. Larvae were reared between salinities of 15–35 and temperatures between 14.5 and 31°C. The greatest percentage survival, growth, development occurred when larvae were reared between 26 and 29°C and between salinities of 30 and 35. Larvae reared outside this salinity and temperature range exhibited reduced growth, survival and/or delayed development. Short‐term (1 h) reduction in larval rearing temperature from 26°C to 23.5°C significantly increased larval metamorphosis without affecting larval survival. Short‐term (1 h) increase in larval rearing temperature from 26°C to 29 and 31°C decreased larval survival and metamorphosis. To ensure repeatability in outcomes, tests showed that larvae sourced from different estuaries did not vary significantly in their metamorphic response to short‐term temperature manipulation and epinephrine‐induced metamorphosis.     

Spatial and temporal patterns in summer ichthyoplankton assemblages on the eastern Bering Sea shelf 1996–2007

Larval and early juvenile fishes were sampled from the eastern Bering Sea (EBS) shelf from 2001 to 2005, and in 2007. Data from these collections were used to examine spatial and temporal patterns in species assemblage structure and abundance. The years 2001–2005 were unusual because the EBS water temperature was ‘warm’ compared with the long‐term mean temperature. In contrast, 2007 was a ‘cold’ year. The abundance of the five most numerous taxa at 12 stations common to all years sampled (1996–2005, 2007) were significantly different among years. Larval and early juvenile stage Theragra chalcogramma (walleye pollock), a commercially important gadid, were by far the most abundant fish in all years. Bottom depth alone best explained assemblage structure in most years, but in others, bottom depth and water column temperature combined and percent sea‐ice coverage were most important. Abundance of T. chalcogramma larvae increases with water column temperature until 5°C and then becomes level. Higher abundances of Gadus macrocephalus (Pacific cod) larvae occur in years with the greatest percent sea‐ice cover as indicated by GAM analysis. Larvae of Lepidopsetta polyxystra (northern rock sole) increase in abundance with increasing maximum wind speed, but decrease at a later date during the last winter storm. The data are consistent with the hypothesis that oceanographic conditions, specifically water temperature and sea‐ice coverage, affect the spatial and temporal pattern of larval abundances. In general, ichthyoplankton species assemblages can be important early indicators of environmental change in the Bering Sea and potentially other subarctic seas as well.     

Albacore (Thunnus alalunga) fishing ground in relation to oceanographic conditions in the western North Pacific Ocean using remotely sensed satellite data

Satellite‐based oceanographic data of sea surface temperature (SST), sea surface chlorophyll‐a concentration (SSC), and sea surface height anomaly (SSHA) together with catch data were used to investigate the relationship between albacore fishing ground and oceanographic conditions and also to predict potential habitats for albacore in the western North Pacific Ocean. Empirical cumulative distribution function and high catch data analyses were used to calculate preferred ranges of the three oceanographic conditions. Results indicate that highest catch per unit efforts (CPUEs) corresponded with areas of SST 18.5–21.5°C, SSC 0.2–0.4 mg m^?3, and SSHA ?5.0 to 32.2 cm during the winter in the period 1998–2000. We used these ranges to generate a simple prediction map for detecting potential fishing grounds. Statistically, to predict spatial patterns of potential albacore habitats, we applied a combined generalized additive model (GAM) / generalized linear model (GLM). To build our model, we first constructed a GAM as an exploratory tool to identify the functional relationships between the environmental variables and CPUE; we then made parameters out of these relationships using the GLM to generate a robust prediction tool. The areas of highest CPUEs predicted by the models were consistent with the potential habitats on the simple prediction map and observation data, suggesting that the dynamics of ocean eddies (November 1998 and 2000) and fronts (November 1999) may account for the spatial patterns of highest albacore catch rates predicted in the study area. The results also suggest that multispectrum satellite data can provide useful information to characterize and predict potential tuna habitats.     

Distribution patterns of loliginid squid paralarvae in relation to the oceanographic features off the South Brazil Bight (22°–25°S)

Loliginid squids constitute marine resources of increasing importance in shelf ecosystems off the coast of South Brazil. However, the existing information and knowledge about the occurrence of early‐life stages and causes of distributional patterns are insufficient. Here, we have revisited Brazilian historical plankton samples obtained from 11 oceanographic surveys to identify paralarvae and their abundances over time. The study area and time period cover the region between Cabo de São Tomé (22°S) and Cananéia (25°S) at depths down to 200 m from 1991 to 2005. Of the 246 paralarvae quantified, ~50% were identified to the genus or species level, including Doryteuthis spp. (D. sanpaulensis and D. plei), Lolliguncula brevis and a single specimen of Pickfordiateuthis pulchella. Paralarval occurrence and abundance peaked in different areas and were associated with distinct oceanographic conditions: D. sanpaulensis occurred in the northern region associated with cold waters and upwelling events, D. plei occurred primarily in the southern region of the study area and in warmer waters, and L. brevis was found in shallow and low salinity waters in the estuarine region off the coast of Santos. Overall, the highest abundance of paralarvae occurred in the nearshore, northernmost areas during summer, and this can be associated with the observed retention mechanisms caused by local circulation, seasonal upwelling, the intrusion of nutrient‐rich waters, and spawning peaks. The present study provides new information and evidence for loliginid patterns in the area that may potentially be useful for better understanding the recruitment patterns and fishery assessments of squid populations.     

Relative influence of static and dynamic features on black‐footed albatross (Phoebastria nigripes) habitat use in central California Sanctuaries

Effective conservation of highly mobile species requires an understanding of the factors that influence their habitat use patterns, locally and within a large‐scale oceanographic context. We characterized the seasonal (chick‐rearing, post‐breeding) and inter‐annual (2004–2008) distribution and abundance of black‐footed albatross (Phoebastria nigripes; BFAL) along the central California continental shelf/slope using standardized vessel‐based surveys. We used a hypothesis‐based information‐theoretic approach to quantify the relative influence of environmental conditions on BFAL occurrence and abundance by assessing their association with: (i) local static bathymetric features, (ii) local and regional dynamic oceanographic processes, and (iii) seasonal and inter‐annual basin‐wide variability. While the presence/absence models yielded stronger results than the abundance models, both revealed that static and dynamic features influence BFAL habitat use. Specifically, occurrence was greatest near the shelf‐break, particularly in months with strong upwelling. High BFAL densities were associated with Rittenburg Bank, especially during the chick‐rearing season, periods of positive North Pacific Gyre Oscillation index and large northern monthly upwelling, evidenced by cool, salty waters in the study area. BFAL aggregation intensity was greatest onshore of the shelf‐break (200 m isobath). Behavioral observations reinforced the notion that transiting BFAL are widely dispersed near the shelf‐break and concentrate in large flocks of birds sitting on the water farther onshore. These results underscore the need to consider oceanographic processes at multiple spatial scales when interpreting changes in BFAL dispersion within marine sanctuaries, and highlight the feasibility of implementing bathymetrically defined protected areas targeting predictable BFAL aggregations within these larger management jurisdictions.     

Dependence of recruitment on parent stock of the spiny lobster,Panulirus argus,in Florida

Despite management practices to achieve sustainability, commercial landings for Florida spiny lobster (Panulirus argus) have experienced a drastic decline (57%) since 2000. This is cause for concern not only for economic reasons, but for issues of sustainability. An annual index of P. argus post‐larval (puerulus) abundance, estimated with a generalized linear model with significant mean sea‐level effects, shows a 36% decrease in annual puerulus supply since 1988. In addition, local Florida spawning stock biomass estimated from an age‐structured sequential population analysis decreased 57% since 1988. Puerulus abundance follows a highly correlated (R = 0.76) trend with a 12‐month delayed spawning stock abundance, which supports the contention that the Florida spawning population is a significant contributing factor to post‐larval recruitment in Florida. Residuals about the puerulus on spawning stock abundance function follow closely an interannual North Atlantic Oscillation Index signal. This residual effect is thought of as a secondary regional population effect on Florida puerulus recruitment. The Florida spiny lobster stock is exploited with no fishing mortality controls due to the Pan Caribbean recruitment concept adopted in Florida spiny lobster management. Therefore, the potential of recruitment overfishing exists if fishing mortality controls to protect local spawning stock abundance, such as catch quotas, are not introduced.     

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.     

Early development and allometric growth in hatchery‐reared Eurasian perch,Perca fluviatilis L.

The morphological development and allometric growth patterns of Eurasian perch, Perca fluviatilis L., a highly valued commercial species, were studied under intensive rearing conditions from hatching up to 50 DPH (Days Post Hatch). Based on the external morphology, four different phases during early development of Eurasian perch were identified: pre‐flexion larva 0–20 DPH (5.70–10.16 mm TL); flexion larva 22–30 DPH (11.09–15.14 mm TL) and post‐flexion larva/juvenile 32–50 DPH (18.00–24.75 mm TL). The results indicate that growth period when final replacement of all temporary (larval) structures and most important changes in the shape of P. fluviatilis occurred (between 13.95 and 24.06 mm TL, during flexion and post‐flexion phase) can be considered as a transitional period between the larva and juvenile. All body segments, except trunk length and tail length showed fast growth (positive allometry) throughout the entire studied period or up to the respective inflexion point with a common tendency to isometry. In addition, the specific behaviours (e.g. pelagic way of life) of Eurasian perch larvae resulted in some characteristic allometric growth patterns in the posterior region, different from the majority of other teleosts. The results are discussed with respect to the ontogeny of the functional morphology under both ecological and aquaculture considerations.     

Use of satellite data to identify critical periods for early life survival of northern shrimp in the Gulf of Maine

The northern shrimp Pandalus borealis is at its southern limit in the Gulf of Maine (GOM), and recruitment success is higher in years with relatively cool water temperature. However, the mechanisms for the temperature effect are not clear. We used rolling window analysis of daily satellite data to identify critical periods for early life survival of the 1998–2012 northern shrimp year‐classes and to investigate the importance of the phenology of the hatch and bloom. Survival was negatively correlated with sea surface temperature (SST) during a 6‐week period around the time of larval emergence (late winter) and during a 4‐week period in late summer when SST and stratification reached annual maxima. Survival was negatively correlated with chlorophyll‐a concentration (chl‐a) during two 5‐week periods centered approximately a month before the hatch midpoint and around the time of settlement to the benthos. A small‐magnitude winter bloom occurred around the time of the hatch in many years, but our results did not reveal a link between survival and bloom‐hatch phenology. The timing of winter and spring blooms were correlated with SST during the preceding 10 months. A survival model including SST and chl‐a during the critical periods explained 73% of the variance in survival. Summer SST increased significantly during the study period; the other critical variables showed no trend. The rolling windows approach revealed sensitive periods in early life history that may not have otherwise been hypothesized, providing a foundation for research towards a greater understanding of processes affecting recruitment.     

Relative importance of gulf and shelf waters for spawning and recruitment of Australian anchovy, Engraulis australis, in South Australia

Gonosomatic indices and egg and larval densities observed from 1986 to 2001 suggest that the peak spawning season of the Australian anchovy (Engraulis australis) in South Australia occurs during January to March (summer and autumn). This coincides with the spawning season of sardine (Sardinops sagax) and the period when productivity in shelf waters is enhanced by upwelling. Anchovy eggs were abundant throughout gulf and shelf waters, but the highest densities occurred in the northern parts of Spencer Gulf and Gulf St Vincent where sea surface temperatures (SST) were 24–26°C. In contrast, larvae >10 mm total length (TL) were found mainly in shelf waters near upwelling zones where SSTs were relatively low (<20°C) and levels of chlorophyll a (chl a) relatively high. Larvae >15 mm TL were collected only from shelf waters near upwelling zones. The high levels of larval abundance in the upwelling zones may reflect higher levels of recruitment to later stages in these areas compared with the gulfs. The sardine spawns mainly in shelf waters; few eggs and no larvae were collected from the northern gulfs. The abundance of anchovy eggs and larvae in shelf waters increased when sardine abundance was reduced by large‐scale mortality events, and decreased as the sardine numbers subsequently recovered. We hypothesize that the upwelling zones provide optimal conditions for the survival of larval anchovy in South Australia, but that anchovy can only utilize these zones effectively when the sardine population is low. At other times, northern gulf waters of South Australia may provide a refuge for the anchovy that the sardine cannot utilize.     

Population structure and movement patterns of blackbelly rosefish in the NE Atlantic Ocean (Azores archipelago)

Blackbelly rosefish Helicolenus dactylopterus (Delaroche, 1809) is one of the most important species of the demersal/deep‐water assemblages fished in the NE Atlantic Ocean (Azores archipelago). However, there is insufficient information about the stock structure of this species to support analytical resource assessments and it is currently managed with a precautionary approach. Here, we examine the depth and temporal distribution, size composition, sex, and movement patterns of blackbelly rosefish in order to test the hypothesis that the stock structure in the Azores region comprises different local management units (MUs). We also evaluate annual abundance indices and size composition from scientific surveys and commercial landings over the past c. 25 years for an assessment of the species' vulnerability to bottom longline fishing pressure. The greatest abundance occurred in seamount areas at 350–800 m depth. Larger individuals were mainly found in deeper waters, and no sexual segregation by depth was observed. Tagging results indicated a strongly sedentary behavior and an intraregional separation among populations. Although the abundance pattern and size composition were very similar over time, this species is particularly vulnerable to overfishing due to its biological characteristics (long life, large size, late maturity, slow growth, and low mortality rate). Proper monitoring and management of its exploitation should be a priority. Exploratory analysis for analytical assessment should be performed under the assumption of local MUs. Further oceanographic research is needed to understand larval transport and mixing of populations.