An Oregon State University (OSU) study that tracked juvenile black rockfish in nearshore waters from 2013 to 2019 has concluded that the young fish fared better than feared in a marine heatwave between 2014 and 2016.
“The study is important for gauging the conditions and making management plans that will affect the species’ survival as the ocean experiences increasing variability because of climate change,” Will Fennie, the study’s lead author and former OSU doctoral student now with NOAA Fisheries, said.
Fennie worked with OSU College of Science researchers Su Sponaugle and Kirsten Grorud-Colvert on the study, which was published March 30 in the journal Scientific Reports.
“Oceanographic conditions dictate water temperature, which influences larval dispersal and food availability — these affect the early growth and survival of fish larvae,” Fennie said. “Larval survival and performance then can influence later life stages — for example, rapid larval growth contributes to increased juvenile survival following settlement to rocky reefs.”
There are many species of rockfish, an ecologically and economically important fish from Baja California to British Columbia. They are known for lifespans that can reach triple digits, an ability to produce prodigious numbers of offspring and variable survival during early stages of their lives, during which they are highly sensitive to environmental conditions.
Adult black rockfish, which can reach more than two feet in length, are dark gray to black on top, with a lighter belly and black spots on their dorsal fins.
Starting at about age 5, a female can release thousands of able-to-swim larvae at a time. While they are developing and growing, juvenile rockfish are an important food source for a range of predators.
Black rockfish are most commonly caught by recreational anglers on the Oregon coast.
Researchers focused on analyzing juvenile black rockfish samples gathered during a long-term collaboration between OSU, the Oregon Department of Fish and Wildlife (ODFW) and the Oregon Coast Aquarium. Samples were collected nearshore from 2013 to 2019, including the period from 2014 and 2016 when those waters were impacted by a marine heatwave.
“The goal was to shed light on how oceanographic conditions affect the early growth and survival of black rockfish,” Fennie explained. “We found that despite fears of doom and gloom with recent anomalous warming of the waters off Oregon’s coast, some young black rockfish grew faster as the temperature increased and surprisingly, there was both high and low survival during different years of the heatwave.”
Researchers found that survival was highest in years characterized by moderate larval growth rates, reduced predation and sufficient food to support growth, Fennie said. Still, when growth was highest, rockfish survival was very low, likely due to a lack of food to sustain that growth, he added.
Several small research grants from OSY’s Hatfield Marine Science Center and Oregon Sea Grant funded the study. The authors also received financial support from the National Science Foundation and the Ocean Science Innovation Fund at OSU.