A small-scaled study provides insight into how fish adapt to future environmental changes

 
 

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Hui-Yu Wang

Climate change and anthropogenic effects have caused pronounced changes in physical habitats and biological functions for marine fishes. The subtropical Pacific Ocean, in particular, is one of the regions with rapid warming rates. At the same time, fishing has led to changes in body size and demography for several Pacific fishes. However, it is difficult to predict changes of fish populations in response to such dual pressures.

Life-history data, such as growth and maturation parameters, provide insight into population response to environmental change. Dr. Hui-Yu Wang’s laboratory initiated a study of life histories for cutlassfishes1 in Taiwan in 2013. In their recent paper2 published in Fishery Bulletin, they compared growth and maturation for the cutlassfish Trichiurus japonicus between the NE and SW coasts. These coasts are with distinct environmental conditions: the NE coast is under the influence of monsoons with low temperature in winter, whereas the SW coast is warm all year round. They found cutlassfish adult growth rates and maximum length were NE > SW, consistent to the Temperature-size rule (i.e., a negative correlation between temperature and body size). Further, cutlassfish length- and age-at-maturation were NE > SW, mainly reflecting phenotypic plasticity due to differential growth between coasts.

An important implication of this study is that environmental changes can drive differential adaptive strategies (e.g., growth and maturation schedules). Thus, these results have implications for climate change ecology and marine resources management. Moreover, these life-history parameters provide as indices for assessing population status, a stepping stone for conservation or fisheries regulation.

These results are congruent to the Theory of Evolution (by Charles Darwin (1859), in: On the Original of Species), describing the process via which natural selection determines the survivor among organisms with differential trait expression. Thus, although developed back in the 19th century, this theory continues being insightful to fisheries resources management today.

1Four cutlassfish species are present in fisheries catch in Taiwan: including 3 species of genus Trichiurus (T. japonicus, T. brevis, and T. lepturus) and Tentoriceps cristatus. Source: Wang, H-Y, CA Dong, H-C Lin. 2017. DNA barcoding of fisheries catch to reveal composition and distribution of cutlassfishes along the Taiwan coast. Fish Res 187: 103-109.

2Wang, H-Y, M Heino. 2018. Adaptive and plastic variation in growth and maturation in the cutlassfish Trichiurus japonicus in subtropical Pacific. Fish Bull 116: 171-182.

 

Figure 1. Length-at-age of cutlassfish at the NE (K) and SW (T) coasts of Taiwan. For immature fish: K < T (upper panel); for adults (middle and lower panels): K > T.

Figure 2. Individual length-and-age data (gray symbols) for cutlassfish at the NE (left panel) and SW (right panel) coast of Taiwan. Yellow symbols are the probabilistic maturation reaction norm (PMRN) estimates with 95% confidence intervals. There was not a significant difference in PMRN estimates between coasts.