A fine-scale multi-step approach to understand fish recruitment variability

Abstract

Recruitment is one of the dominant processes regulating fish population productivity. It is, however, notoriously difficult to predict, as it is the result of a complex multi-step process. Various fine-scale drivers might act on the pathway from adult population characteristics to spawning behaviour and egg production, and then to recruitment. Here, we provide a holistic analysis of the Northwest Atlantic mackerel recruitment process from 1982 to 2017 and exemplify why broad-scale recruitment–environment relationships could become unstable over time. Various demographic and environmental drivers had a synergetic effect on recruitment, but larval survival through a spatio-temporal match with prey was shown to be the key process. Recruitment was also mediated by maternal effects and a parent–offspring fitness trade-off due to the different feeding regimes of adults and larvae. A mismatch curtails the effects of high larval prey densities, so that despite the abundance of food in recent years, recruitment was relatively low and the pre-existing relationship with overall prey abundance broke down. Our results reaffirm major recruitment hypotheses and demonstrate the importance of fine-scale processes along the recruitment pathway, helping to improve recruitment predictions and potentially fisheries management.

Impact of the Strong Downwelling (Upwelling) on Small Pelagic Fish Production during the 2016 (2019) Negative (Positive) Indian Ocean Dipole Events in the Eastern Indian Ocean off Java

“…Furthermore, the significant cross-correlation between the Chl-a and small pelagic fish catch had a time lag of one-year (11-13 months), which can be attributed to the larvae of fish often reaching their first feeding stage at approximately the same time that phytoplankton blooms occur [35,36]. Strong downwelling (upwelling) during nIOD (pOD) phases causes low (high) Chl-a, which may result in decrease (increase) fish recruitment through the match (mismatch) [37,38], because the key element in larval survival is often the availability of food [39,40]. Availability of plankton in sufficient quantities at the right spatiotemporal scale enhances the larval survival rate.…”

“…Availability of plankton in sufficient quantities at the right spatiotemporal scale enhances the larval survival rate. Further investigation is necessary to understand how the enhanced phytoplankton production during pIOD and other relevant environmental drivers interacts with the life cycle and influences the recruitment of the small pelagic fish and the interannual variability of the fish catch, in the Palabuhanratu Bay [37,38].…”

Cold offshore area provides a favorable feeding ground with lipid‐rich foods for juvenile Japanese sardine

“…Furuichi et al (2020) hypothesized that the eggs spawned away from Kyushu Island tended to be transported to the offshore area because of the flow patterns of the TWC. Hence, inhabiting the offshore area might be achieved by passive transportation during the egg and larval stages (Ito et al, 2009; Kasai et al, 1997) and thus may favor sardine early life stages survival and recruitment due to favorable feeding conditions (Nishikawa et al, 2013; also see Ferreira et al, 2020; Brosset et al, 2020 for other fish species). Otherwise, the juvenile sardine could actively migrate to the offshore area from the coastal area.…”

“…Since the maturity of juvenile sardine in the next spring depends on the nutritional condition during the summer (Morimoto, 2010; Yoneda et al, 2013), food availability is an important factor to elucidate their population dynamics (Brosset et al, 2020; Ferreira et al, 2020). The offshore area could allow the sardine to store more lipids while maintaining a higher growth rate because the mass‐specific metabolic rate is generally lower for bigger individuals than for smaller ones (Post & Lee, 1996).…”

“…Recruitment, which is the result of the number of eggs spawned and their survival, is a key component of population dynamics of marine exploited fishes. Various demographic and environmental drives have a synergetic effect on recruitment, as shown by the density‐dependent effects on egg production, the maternal effects, and the effects of spatiotemporal overlap between fish larvae and their prey (Brosset et al, 2020; Ferreira et al, 2020; Takasuka et al, 2019a, b). The ecological mechanism of biomass fluctuations in the Japanese sardine has been debated, and it is often attempted to be explained by a changing climate (Chavez et al, 2003; Kawasaki, 1992; Nakayama et al, 2018).…”