Climate, Anchovy, and Sardine

Stock level of Japanese sardine (Sardinops melanostictus) was high from 1980s to early 1990s and low from late 1990s to 2000s. The warm and cold water masses in the vicinity of the Kuroshio axis from winter to early spring used to be critical for the recruitment in the high‐stock period, because most of the larvae were distributed there. However, the environmental fluctuation might not affect the recruitment in the low‐stock period. Some studies reported that spawning location and spawning season, and hence the larval habitat, differ depending on the stock level. Three points were investigated in this study: (a) how spawning location and spawning season shifted from the late 1990s, (b) confirmation of the distribution area of larvae in the recent low‐stock period and (c) whether the water temperature in the vicinity of the Kuroshio axis was still related to the recruitment in the low‐stock period. The spawning location and spawning season clearly changed after 1995. Consequently, particle tracking experiments suggested that the larvae appeared in the vicinity of the Kuroshio axis from winter to early spring decreased. Nevertheless, only the ambient temperature of larvae that appeared in the vicinity of the Kuroshio axis from winter had a significant negative correlation with an index of the recruitment in the low‐stock period. It is suggested that the warm and cold masses in the vicinity of the Kuroshio axis are critical for the recruitment regardless of the stock level.

Section: Discussionmentioning

confidence: 99%

Relationship between recruitment of Japanese sardine (Sardinops melanostictus) and environment of larval habitat in the low‐stock period (1995–2010)

Nishikawa

2018

“…In particular, the spawning grounds of small pelagic fishes are known to expand or contract following changes in abundance of the reproductive stock (Checkley, Jr, Alheit, Oozeki, & Roy, ; Giannoulaki et al, ; Saraux et al, ). The populations of small pelagics are naturally subject to strong abundance fluctuations (Checkley, Asch, & Rykaczewski, ) which may be more pronounced in those species under heavy fisheries exploitation, where age class structure is usually truncated with very low individuals in age classes beyond 1‐ or 2‐year‐olds. Changes in the location and extent of spawning habitat for species of commercial interest have received a lot of research attention (inter alia, Brosset et al, ; Giannoulaki et al, ; Saraux et al, ).…”

Section: Introductionmentioning

confidence: 99%

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

Maynou

Sabatés

Raya

2020

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.

“…Several studies have demonstrated clear top‐down fishing effects on forage fish, usually exemplified by the dramatic collapses of commercially important small pelagic fish stocks of herring, sardines and anchovies (e.g., Coetzee, van der Lingen, Hutchings, & Fairweather, ; Dragesund, Hamre, & Ulltang, ; Fréon, Bouchon, Mullon, García, & Ñiquen, ). In addition, bottom‐up forcing, mediated through direct physiological responses to environmental factors or indirect responses to climate‐driven changes in the composition and availability of zooplankton prey has been shown to underlie large‐scale fluctuations of forage fish, such as the alternating dominance of sardines and anchovies in upwelling systems (Baumgartner et al., ; Schwartzlose et al., ; Alheit & Niquen, ; Van der Lingen, Hutchings, & Field, ; Checkley, Asch, & Rykaczewski, ). Although many studies have identified single drivers, the potential synergy of multiple internal and external factors in regulating population dynamics of forage fish, as well as their relative importance throughout ontogeny is a largely unresolved issue (Hjermann, Ottersen, & Stenseth, ; Lindegren & Checkley, ; Lindegren, Östman, & Gårdmark, ).…”

Section: Introductionmentioning

confidence: 99%

Productivity and recovery of forage fish under climate change and fishing: North Sea sandeel as a case study

Lindegren

Deurs

MacKenzie

et al. 2017

Forage fish occupy a central position in marine food‐webs worldwide by mediating the transfer of energy and organic matter from lower to higher trophic levels. The lesser sandeel (Ammodytes marinus) is one of the ecologically and economically most important forage fish species in the North‐east Atlantic, acting as a key prey for predatory fish and sea birds, as well as supporting a large commercial fishery. In this case study, we investigate the underlying factors affecting recruitment and how these in turn affect productivity of the North Sea sandeel using long‐term data and modelling. Our results demonstrate how sandeel productivity in the central North Sea (Dogger Bank) depends on a combination of external and internal regulatory factors, including fishing and climate effects, as well as density dependence and food availability of the preferred zooplankton prey (Calanus finmarchicus and Temora longicornis). Furthermore, our model scenarios suggest that while fishing largely contributed to the abrupt stock decline during the late 1990s and the following period of low biomass, a complete recovery of the stock to the highly productive levels of the early 1980s would only be possible through changes in the surrounding ecosystem, involving lower temperatures and improved feeding conditions. To that end, we stress the need for ecosystem‐based management accounting for multiple internal and external factors occurring within the broader context of the ecosystem in which forage fish species, such as sandeel, play an important and integral part.