Causal effects of population dynamics and environmental changes on spatial variability of marine fishes

Abstract

Populations with homogeneous distributions have better bet-hedging capacity than more heterogeneously distributed populations. Both population dynamics and environmental factors may influence the spatial variability of a population, but clear empirical evidence of such causal linkages is sparse. Using 25-year fish survey data from the North Sea, we quantify causal effects of age structure, abundance, and environment on nine fish species. We use empirical dynamic modeling-an approach based on state-space reconstruction rather than correlation-to demonstrate causal effects of those factors on population spatial variability. The causal effects are detected in most study species, though direction and strength vary. Specifically, truncated age structure elevates population spatial variability. Warming and spatially heterogeneous temperatures may enhance population spatial variability, whereas abundance and large-scale environmental effects are inconclusive. Fishing may affect population spatial variability directly or indirectly by altering age structure or abundance. We infer potential harmful effects of fishing and environmental changes on fish population stability, highlighting the importance of considering spatial dynamics in fisheries management.

Age‐specific habitat preference, carrying capacity, and landscape structure determine the response of population spatial variability to fishing‐driven age truncation

“…They have found negative relationships for Pacific sardine and Pacific chub mackerel at multiple time lags, Pacific hake at time lag of 11 years, and no relationship for bocaccio. Similarly, among eight exploited fish species on the North Sea, only Atlantic cod, plaice, and Atlantic mackerel exhibited negative causal relationships between age diversity and spatial variability of fish (Wang et al, 2020). Our findings from the individual-based model suggest that within the same marine ecosystem, the variability in species' spatial responses to age truncation is likely associated with their degree of age-specific habitat preference.…”

“…Such an increase in variability in local abundances leads to an elevated population spatial variability at the landscape scale. This mechanism may explain empirical findings of the negative association between age structure and spatial variability of fishes (Kuo et al, 2016;Wang et al, 2020).…”

“…In the same study, potential redistribution in the physical environment and resource availability has also been predicted to further influence fish distribution. An empirical study by Wang et al (2020) the relationship is reversed for Atlantic cod. Thus, while changing climate can directly influence fish spatial dynamics by reducing population size, its indirect impacts on carrying capacity and habitat structure and the resulting fish spatial distribution require more attention.…”

“…Empirical work has further found that species differ in how their spatial distribution responds to fishing-induced age truncation (Kuo et al, 2016;Wang et al, 2020), yet the underlying mechanism remains largely unknown.…”

Hump‐shaped relationship between aggregation tendency and body size within fish populations

“…In contrast, whiting, haddock and saithe exhibit apparently humped shape relationship in both quarters yet with different steepness. Such differences suggested that the aggregation tendency not only could be affected by body size, but might also be determined by other biological traits, migratory behavior and fishing pressure at the species level (Kuo et al 2016, Wang et al 2020). For example, the different pattern between Q1 and Q3 for the pelagic species (herring, mackerel and sprat) might because they can quickly aggregate during spawning season while dispersing during the resting season (Daan et al 1990).…”