Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks. Disentangling the effects of environment and stock has proven to be problematic and has resulted in recurrent controversy between studies supporting either hypothesis. In the present study, we examine the relationship between interannual changes in temperature and variation in recruitment for nine Atlantic cod (Gadus morhua) stocks in the North Atlantic. We show that for individual stocks, the relationship often appears weak and statistically not significant. On the other hand, by combining in a single metaanalysis the results from individual stocks, we demonstrate that recruitment of Atlantic cod is linked to interannual fluctuations in temperature in such a way that for stocks located in warm water the relationship is negative, for stocks located in cold water the relationship is positive, and there is no relationship for stocks located in the middle of the temperature range.

ABSTRACT

Knowledge of the spatial distribution of fish assemblages biodiversity and structure is essential for prioritizing areas of conservation. Here we describe the biodiversity and community structure of demersal fish assemblages and their habitat along the northeast Brazilian coast by combining bottom trawl data and underwater footage. Species composition was estimated by number and weight, while patterns of dominance were obtained based on frequency of occurrence and relative abundance. A total of 7,235 individuals (830 kg), distributed in 24 orders, 49 families and 120 species were collected. Community structure was investigated through clustering analysis and by a non-metric multidimensional scaling technique. Finally, diversity was assessed based on six indices. Four major assemblages were identified, mainly associated with habitat type and depth range. The higher values of richness were found in sand substrate with rocks, coralline formations and sponges (SWCR) habitats, while higher values of diversity were found in habitats located on shallow waters (10-30m). Further, assemblages associated with sponge-reef formations presented the highest values of richness and diversity. In management strategies of conservation, we thus recommend giving special attention to SWCR habitats, mainly those located on depths between 30-60 m. This can be achieved by an offshore expansion of existing MPAs and/or by the creation of new MPAs encompassing those environments.

Species of the family Sternoptychidae (hatchetfishes) occur worldwide and play critical roles by sequestering carbon, recycling nutrients, and acting as a key trophic link between epipelagic primary consumers and higher trophic levels in marine ecosystems. Nevertheless, basic knowledge on their ecology is still lacking and their functional ecology remains understudied with respect to composition, organization, functions and environment interactions. Here we integrated comprehensive information collected in the western Tropical Atlantic on the diversity, abundance, distribution and trophic ecology of hatchetfishes, including physicochemical features of their habitats and extensive carbon and nitrogen stable isotope data on its main prey groups. On this basis we defined five functional groups of hatchetfishes with different diet preference, isotopic composition, and vertical abundance peaks and reveal a possible high resource partitioning. Additionally, these species might have a different feeding tie chronology. Hence, hatchetfishes segregate in different ecological groups responding differently to environmental constraints including oxygen concentration and presenting diverse functional roles. As deep-sea species that migrate to epipelagic waters, hatchetfishes may play a key role in the transfer of sub-surface photoassimilated carbon to deeper waters, a pathway through which the effects of climate change at the surface are transferred to the deep ocean. Moreover, as consumers of gelatinous organisms, these species convert "gelatinous energy" into "fish energy" readily usable by higher trophic levels, including endangered and commercially important species. This is a crucial trophic relationship that has been historically underestimated due to methodology limitations (e.g., quickly digested gelatinous organisms were probably underestimated in previous studies, based solely on stomach contents). Considering in ecosystem models this trophic relationship, as well as the functional organization of hatchetfishes, is important to properly answer important ecological questions including resource use, carbon transportation, and influence of mesopelagic community in climate change process.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. Highlights ► Hatchetfishes were divided into five functional groups. ► Hatchetfishes have different diet, isotopic composition, and vertical distribution. ► Hatchetfishes are differently distributed in relation to oceanographic features. ► Hatchetfishes forage more on gelatinous organisms than previously thought. ► Hatchetfishes play a key role in the transfer of photoassimilated carbon to deeper waters.

The performance of 20 fishery production systems off the state of Para´in the northern region of Brazil was compared using the ÔRAPFISHÕ methodology, with 57 identified attributes distributed among five evaluation fields: economics, sociology, ecology, technology and politics. The results indicated the existence of three large groups of fishery sectors: (i) industrial (red snapper with traps, the Laulao catfish, shrimp trawl) and semi-industrial (lobster) fisheries; (ii) large-scale artisanal fisheries (acoupa weakfish, red snapper with lines, king mackerel, Spanish mackerel, coco sea catfish); and (iii) smallscale artisanal fisheries (shellfish, crab, estuarine longline, fish traps, etc.). While the industrial and large-scale artisanal systems demonstrated greater sustainability from an economic and social standpoint, small-scale fisheries appeared to be more ecologically sustainable. Based on the results, a reduction in industrial fishing efforts is recommended, along with the establishment of licensing quotas for fishing vessels, as well as an increased investment in research on proper guidance and management of the semi-industrial and large-scale artisanal fisheries sectors. For small-scale artisanal fisheries, economic incentives are suggested for the aggregate value of the products and to assist fishers in the development of an appropriate social organization. Finally, it is believed that a greater stakeholder involvement in the decision-making process would improve management actions for all modalities.

This study describes the biological importance of Guajará Bay (Belém, Pará, Brazil) for fish fauna and presents a diagnosis of water quality in the main channel and creeks, using the icthyofauna as an ecological indicator. A total of 567 individuals from 40 species were identified. About 58% of these use Guajará Bay as a nursery ground, 49 and 81% use the bay as a breeding and feeding ground, respectively. There were no significant differences between environments as measured by the diversity index; however, fish relative abundance (catch per unit of effort) was greater in the creeks than in the main channel. A significant difference was detected in the fish fauna inhabiting the main channel compared with the creeks. In the main channel, icthyofauna significantly differed during December relative to other months.

We developed an Ecopath model in the Estuary of Sirinhaém River (SIR), a small-sized system surrounded by mangroves, subject to high impact, mainly by sugar cane industry and other farming industries in order to describe the food web structure and trophic interactions. In addition, we compared our findings with those of 20 available Ecopath estuarine models for tropical, subtropical and temperate regions, aiming to synthesize the knowledge on trophic dynamics and provide a comprehensive analysis of the structures and functioning of estuaries. Our model consisted of 25 compartments and its indicators were within the expected range for estuarine areas around the world. The average trophic transfer efficiency for the entire system was 11.8%, similar to the theoretical value of 10%. The Keystone Index and MTI (Mixed Trophic Impact) analysis indicated that the snook (Centropomus undecimalis and Centropomus parallelus) and jack (Caranx latus and Caranx hippos) are considered as key resources in the system, revealing its high impact in the food web. Both the species have a high ecological and commercial relevance, despite the unregulated fisheries. As result of the comparison of ecosystem model indicators in estuaries, differences in the ecosystem structure from the low latitude zones (tropical estuaries) to the high latitude zones (temperate system) were noticed. The structure of temperate and sub-tropical estuaries were based on high flows of detritus and export, while tropical systems have high biomass, respiration and consumption rates. Higher values of System Omnivory Index (SOI) and Overhead (SO) were observed in the tropical and subtropical estuaries, denoting a more complex food chain. Globally, none of the estuarine models were classified as fully mature ecosystems, although the tropical ecosystems were considered more mature than the subtropical and temperate ecosystems. This study is an important contribution to the trophic modeling of estuaries, Highlights ► Sirinhaém estuary, Northeast Brazil, is an immature and resilient ecosystem. ► The jack and, mainly, snook were key species in the Estuary of Sirinhaém River. ► Tropical estuaries were based in high biomass, respiration and consumption rates. ► The System Overhead Index was higher in tropical estuaries than in the other systems. ► TPP/TR was lower in tropical estuaries than in the other systems.

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