Dynamics of juvenile salmon and forage fishes in nearshore kelp forests

Abstract

North‐east Pacific juvenile salmon and forage fishes, including the endangered salmon species Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch), chum (Oncorhynchus keta), and pink (Oncorhynchus gorbuscha), and the forage fishes species of Pacific herring (Clupea pallasi), surf smelt (Hypomesus pretiosus), and sand lance (Ammodytes hexapterus), utilize kelp environments. Many details of the kelp forest ecosystem function for these fishes are lacking. Kelp forests, salmon, and forage fishes are declining precipitously as the global climate shifts and developments along coastal shorelines expand. It is therefore essential to understand kelp forest function for these species. Analysis of 7 years of snorkelling survey videos indicates that both forage fishes and salmon use kelp forests throughout the outmigration season, and that their interactions occur in small and large groups, primarily along the outer edge of kelp beds. Over the course of outmigration, juvenile Chinook and coho salmon encounter sand lance first, followed by smelt and herring. The majority of interactions are intermingling, in which a subset proceed to predation, primarily on herring. It is important to develop and implement specific fishery and habitat conservation measures to preserve and restore these functions. Long‐term research has shown that intact, conserved nearshore habitats function better ecologically than restored habitats, and individual kelp forests can function differently for forage fishes and salmon. Therefore, conservation plans should be developed to conserve wild kelp forests which are documented to provide ecosystem function for salmon and forage fishes, by protecting them from various development impacts, including dredging, filling, and water‐quality decline. Coastal restoration is often only successful when ecosystem‐limiting factors that result in a loss of habitat are resolved. Kelp forest restoration, therefore, should be prioritized for regions of known high historical kelp forest importance, with restoration actions focused on correcting the limiting factors that caused loss and/or degradation.

Experimentally Determining Optimal Conditions for Mapping Forage Fish with RPAS

“…A variety of methods can be used to quantify the abundance and distribution forage fish, but many cannot access shallow areas, are size selective or destructive, and are subject Drones 2022, 6, 426 2 of 21 to fish avoidance [1,18]. By comparison, RPAS offer a non-destructive, cost and time effective method to survey tens of square kilometers of shallow nearshore habitats that are important to small surface schooling forage fish species such as Sand Lance and Pacific Herring [19,20].…”