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Albo-Puigserver, M., Munoz, A., Navarro, J., Coll, M., Pethybridge, H., Sanchez, S., et al. (2017). Ecological energetics of forage fish from the Mediterranean Sea: Seasonal dynamics and interspecific differences. Deep-Sea Res. Part II-Top. Stud. Oceanogr., 140, 74–82.
Résumé: Small and medium pelagic fishes play a central role in marine food webs by transferring energy from plankton to top predators. In this study, direct calorimetry was used to analyze the energy density of seven pelagic species collected over four seasons from the western Mediterranean Sea: anchovy Engraulis encrasicolus, sardine Sardina pilchardus, round sardinella Sardinella aurita, horse mackerels Trachurus trachurus and T. mediterraneus, and mackerels Scomber scombrus and S. colias. Inter-specific differences in energy density were linked to spawning period, energy allocation strategies for reproduction and growth, and feeding ecologies. Energy density of each species varied over time, with the exception of S. colitis, likely due to its high energetic requirements related to migration throughout the year. In general, higher energy density was observed in spring for all species, regardless of their breeding strategy, probably as a consequence of the late-winter phytoplankton bloom. These results provide new insights into the temporal availability of energy in the pelagic ecosystem of the Mediterranean Sea, which are pivotal for understanding how the population dynamics of small and medium pelagic fishes and their predators may respond to environmental changes and fishing impacts. In addition, the differences found in energy density between species highlighted the importance of using species specific energy values in ecosystem assessment tools such as bioenergetic and food web models.
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Bauer, R. K., Forget, F., & Fromentin, J. - M. (2015). Optimizing PAT data transmission: assessing the accuracy of temperature summary data to estimate environmental conditions. Fish Oceanogr., 24(6), 533–539.
Résumé: Pop-up archival tags (PAT) provide summary and high-resolution time series data at predefined temporal intervals. The limited battery capabilities of PATs often restrict the transmission success and thus temporal coverage of both data products. While summary data are usually less affected by this problem, as a result of its lower size, it might be less informative. We here investigate the accuracy and feasibility of using temperature at depth summary data provided by PATs to describe encountered oceanographic conditions. Interpolated temperature at depth summary data was found to provide accurate estimates of three major thermal water column structure indicators: thermocline depth, stratification and ocean heat content. Such indicators are useful for the interpretation of the tagged animal's horizontal and vertical behaviour. The accuracy of these indicators was found to be particularly sensitive to the number of data points available in the first 100m, which in turn depends on the vertical behaviour of the tagged animal. Based on our results, we recommend the use of temperature at depth summary data as opposed to temperature time series data for PAT studies; doing so during the tag programming will help to maximize the amount of transmitted time series data for other key data types such as light levels and depth.
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Benazzouz, A., Pelegri, J. L., Demarcq, H., Machin, F., Mason, E., Orbi, A., et al. (2014). On the temporal memory of coastal upwelling off NW Africa. J. Geophys. Res.-Oceans, 119(9), 6356–6380.
Résumé: We use a combination of satellite, in situ, and numerical data to provide a comprehensive view of the seasonal coastal upwelling cycle off NW Africa in terms of both wind forcing and sea surface temperature (SST) response. Wind forcing is expressed in terms of both instantaneous (local) and time-integrated (nonlocal) indices, and the ocean response is expressed as the SST difference between coastal and offshore waters. The classical local index, the cross-shore Ekman transport, reproduces reasonably well the time-latitude distribution of SST differences but with significant time lags at latitudes higher than Cape Blanc. Two nonlocal indices are examined. One of them, a cumulative index calculated as the backward averaged Ekman transport that provides the highest correlation with SST differences, reproduces well the timing of the SST differences at all latitudes (except near Cape Blanc). The corresponding time lags are close to zero south of Cape Blanc and range between 2 and 4 months at latitudes between Cape Blanc and the southern Gulf of Cadiz. The results are interpreted based on calculations of spatial and temporal auto and cross correlations for wind forcing and SST differences. At temporal scales of 2-3 weeks, the alongshore advection of alongshore momentum compensates for interfacial friction, allowing the upwelling jet and associated frontal system to remain active. We conclude that the coastal jet plays a key role in maintaining the structure of coastal upwelling, even at times of relaxed winds, by introducing a seasonal memory to the system in accordance with the atmospheric-forcing annual cycle.
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Boyd, C., Grunbaum, D., Hunt, G. L., Punt, A. E., Weimerskirch, H., & Bertrand, S. (2017). Effects of variation in the abundance and distribution of prey on the foraging success of central place foragers. J. Appl. Ecol., 54(5), 1362–1372.
Résumé: 1. Seabirds and pinnipeds are vulnerable to reductions in prey availability, especially during the breeding season when spatial constraints limit their adaptive capacity. There are growing concerns about the effects of fisheries on prey availability in regions where large commercial fisheries target forage fish. 2. For breeding seabirds and pinnipeds, prey availability depends on a combination of abundance, accessibility, patchiness and distance from the colony. An understanding of the aspects of prey availability that determine foraging success is essential for the design of effective management responses. 3. We used a mechanistic individual-based foraging model based on observed data for two sea-bird species, the Peruvian Booby Sula variegata and Guanay Cormorant Phalacrocorax bougainvilliorum, to simulate the foraging patterns of seabirds feeding on schooling fish. We ran the model over simulated prey fields representing eight possible combinations of high or low prey abundance, shallow or deep prey, and broadly distributed or spatially concentrated prey. 4. The results highlight the importance of the accessibility of prey. Depth distribution was the primary factor determining modelled foraging success for both species, followed by abundance, and then spatial configuration. 5. Synthesis and applications. The individual-based foraging model provides a spatially explicit framework for assessing the effects of fisheries on the foraging success of seabirds and other central place foragers, and for evaluating the potential effectiveness of marine-protected areas and other fisheries management strategies for safeguarding central place foragers in dynamic ecosystems. Our analysis indicates that broad-scale fisheries management strategies that maintain forage fish above critical biomass levels are essential, but may need to be supplemented by targeted actions, such as time-area closures, when environmental conditions lead to low prey abundance or reduce prey accessibility for seabirds or pinnipeds of conservation concern. The individual-based foraging model is adaptable and could be reconfigured for application to other species and systems.
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Brosset, P., Lloret, J., Munoz, M., Fauvel, C., Van Beveren, E., Marques, V., et al. (2016). Body reserves mediate trade-offs between life-history traits: new insights from small pelagic fish reproduction. R. Soc. Open Sci., 3(10), 160202.
Résumé: Limited resources in the environment prevent individuals from simultaneouslymaximizing all life-history traits, resulting in trade-offs. In particular, the cost of reproduction is well known to negatively affect energy investment in growth and maintenance. Here, we investigated these trade-offs during contrasting periods of high versus low fish size and body condition (before/after 2008) in the Gulf of Lions. Female reproductive allocation and performance in anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) were examined based onmorphometric historical data from the 1970s and from 2003 to 2015. Additionally, potential maternal effects on egg quantity and quality were examined in 2014/2015. After 2008, the gonadosomatic index increased for sardine and remained steady for anchovy, while a strong decline in mean length at first maturity indicated earlier maturation for both species. Regarding maternal effects, for both species egg quantity was positively linked to fish size but not to fish lipid reserves, while the egg quality was positively related to lipid reserves. Atresia prevalence and intensity were rather low regardless of fish condition and size. Finally, estimations of total annual numbers of eggs spawned indicated a sharp decrease for sardine since 2008 but a slight increase for anchovy during the last 5 years. This study revealed a biased allocation towards reproduction in small pelagic fish when confronted with a really low body condition. This highlights that fish can maintain high reproductive investment potentially at the cost of other traits which might explain the present disappearance of old and large individuals in the Gulf of Lions.
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