How Ocean Conditions Change Rockfish Reproduction

Recent NOAA National Marine Fisheries Service-Sea Grant Fellow Sabrina Beyer, describes her research into how ocean conditions affect rockfish reproduction. 

TELL US ABOUT YOUR BACKGROUND AND HOW YOU DECIDED ON THIS RESEARCH PROJECT.

I am finishing my PhD this quarter at UC Santa Cruz in the department of Ecology and Evolutionary Biology, but some of this research stems from collaborations with the NOAA Southwest Fisheries Science Center, which is located on the coastal marine science campus at UC Santa Cruz. I was partnering with them on life history studies of federally managed marine fish species before I became a graduate student.

We were looking at how fish grow and how they reproduce and then why differences in growth and reproduction might be important for management. Early on I got involved in a project with rockfishes, which are a tremendously diverse group of fishes that occur all along the US West Coast. There are over 65 species that are found off the coast of California – which is really cool. NOAA Fisheries is interested in them because they are fished both commercially and recreationally. They're economically important, but also socially and culturally important. 

Some of these rockfishes can live over 100 years, although those tend to be more northern or deeper water species. And some don't live that long: only about 35 years or so. I've gotten involved with this life history work to better understand the population dynamics – the study of how populations change through time – and how the environment may influence how these fish grow and reproduce. 

WHAT IS THE MAIN QUESTION YOUR RESEARCH ADDRESSES?

What we were seeing is that among some rockfish species in Southern California, females would produce broods of larvae multiple times a year. This is interesting because up north, they only reproduce once per year. We were trying to understand, “well, why is this happening and how might this affect population dynamics?” 

We wanted to know how different environmental conditions along the coast might influence production. So: why fish are doing something different in the north than they're doing in the south. But also through time. We know that ocean conditions off the coast of California change each year, and we wanted to know how those changes influence the number of energy reserves that these females have and the number of larvae that they produce each year.

Rockfishes are really interesting because they are livebearers. The males and females mate, and then the females internally fertilize their eggs. Females gestate embryos for a couple of weeks to a month or so, and they release these tiny little larvae.

These tiny little larvae have little fins, and they can feed and swim right away. 

Most fish just release gametes – sperm and eggs – into the wild, and then there's external fertilization. But female rockfish are really investing a lot of energy into reproduction. They can produce anywhere from 15,000 to over 2 million larvae in a brood depending on the size of the female and the species.

HOW DID YOU DO IT?

Our methods were to sample rockfish off the central coast of California over the winter when most are reproducing. We partnered with the local fishing community to collect certain species by hook-and-line, using their expert knowledge. In doing so, we were able to develop a time series — for at least one species — of 21 years of data to learn how these fish were reproducing through time. We have data on what the environmental conditions were and on the body condition of the fish, which was a proxy for energy reserves and is basically a measure of how fat they were. Also, we were able to collect gonads and count the number of larvae that these fish were producing each year. 

We ended up with enough data to look at reproduction in four different species. We looked at yellowtail and widow rockfish and also bocaccio and chili pepper. I think they got the name chili pepper because fishers used to catch them on longlines in deep water. They'd have all these hooks and when the fish came up from depth, their swim bladders would expand and the fish would float at the surface. You'd see a long line of these beautiful, bright red fish on the string, and they look like little red peppers.

WHAT DID YOU FIND?

Really, the finding of the study was that yes, reproduction is highly variable from year to year in these species. That seems simple, but it's something we didn't know before. 

I've also learned that food is really important  And sometimes increased food resources can even balance some of the effects of warmer temperatures on higher metabolic rates. If there's enough food in the water, the fish can counteract the extra metabolic costs of warm water, up to a point. So I've learned that both temperature and food resources are really important to reproduction and the energy needed to reproduce.

Interestingly, we found that a large female yellowtail rockfish in a really good year will be expected to produce over 2 million larvae in a single brood. But in a really bad year only about 770,000. That amounts to an over 60% reduction in their reproductive effort. That, to me, is incredible because that's a single fish producing millions fewer larvae in a bad year compared to a good year.

We're finding that the productive effort of these females can vary greatly from year to year and also through space, depending on where they live along the coast. This is really interesting because this variability isn’t something that has been put into many of the population models but is important to their life history.

So that has been eye-opening in thinking about how such strong variation in the reproductive effort of individuals may influence population dynamics as ocean conditions change off our coast, and thinking about spatial variation in the reproductive productivity of different groups of individuals that occur from north to south in the California Current Ecosystem.

WHAT DOES THIS MEAN FOR MANAGEMENT?

The next step is to better understand how reproductive variability might affect overall fisheries productivity. This is something that we would like to incorporate into what we call stock assessments — when we're assessing the health and the status of these fish populations and trying to figure out different fishing limits to ensure that fisheries are sustainable through time. 

The research for this project demonstrated that phenotypic plasticity exists for these species. That's when a life history trait, such as how much these fish reproduce and how frequently, changes based on environmental conditions. So we're understanding that yes, phenotypic plasticity in reproductive traits exists, and this is how reproductive output is influenced by the environment. 

A next step would be trying to understand how variation in reproductive effort affects recruitment, and then population dynamics. That would be a great next step.

Beyer recently finished her PhD at the University of California, Santa Cruz and will begin a postdoc at the University of Washington in January.