Rockfish Recruitment and the Ocean Environment
Southwest Fisheries Science Center, National Marine Fisheries Service
3150 Paradise Drive, Tiburon, California 94920
As Jo Guerrero mentioned, I work for National Marine Fisheries Service in Tiburon, and one of the primary missions of National Marine Fisheries Service is to provide scientific support to the nation's Fishery Management Councils. These Councils, you may or may not be aware, were established in 1976 with passage of the Magnuson Act that extended our fisheries jurisdiction out 200 miles. With that extension, we acquired a lot of responsibility for managing our marine resources. National Marine Fisheries Service plays a large role in giving scientific information to these councils so that they can adequately manage and conserve our large commercial fisheries. You may know that on a national scale there have been some catastrophic failures in fisheries management. In the northeast part of the country, the New England Fishery Management Council did not take a very cautious approach to resource management, and now there has been a total collapse of cod, haddock, and summer flounder fisheries in that part of the world. I think it is very unfortunate that this occurred the way it did, because managers in that part of the world could have more effectively utilized the type of scientific advice they were being given by agencies like my own.
I'm happy to report, though, that the situation is not nearly so dismal here on the west coast. As you have heard, I am also a member of the Groundfish Management Team for the Pacific Fishery Management Council. Let's see if I can start with my first graph [Figure 1]. In it you can see the rockfish catch along the west coast from 1986 to 1994. This includes catches of the genera Sebastes, which includes the rockfishes, and Sebastolobus, which are the thornyheads. During this time period, from 1986 to 1995, landings have averaged about 35,000 metric tons of fish per year. That's really quite a lot of fish! These fish go toward feeding the nation's public and that's why we're in business doing the stock assessments that we do. Here on the west coast, rockfish landings have been very stable, and the fishery has been very productive. It's important to understand the source of the productivity in these stocks. It is not due to the growth of individual fish putting on biomass, rather the productivity of rockfish stocks is mainly due to the periodic creation of very strong year classes that progress through the fishery and sustain it for a number of years. This is the so-called year-class strength or recruitment paradigm in fisheries. So, rockfish are very extreme in this regard, in terms of year-class strength. We have observed rockfish reproductive success varying from one year to the next by as much as two orders of magnitude.
I'll illustrate this with my next slide of widow rockfish [Figure 2], which is one of the mainstays of the west coast groundfish fishery. In this graph I show recruitment on the Y- axis from 1975 to 1990; in the upper right portion of the figure you can see landings in the fishery, which have averaged about 8,000 metric tons per year. One can see how variable recruitment has been. In my talk, when I use the term recruitment, I am referring to it strictly in the fisheries sense, and that is the actual number of age five fish that become available to the commercial fishery. Because widow rockfish grow very slowly, they don't reach a large enough size to be exploited by the trawl fishery until they are five years old. So, the two strong year classes evident in 1985 and 1986 are actually age five fish, and they represent the reproduction that actually occurred in 1980 and 1981.
So, this demonstrates the quandary that fisheries managers face when trying to manage a fishery like this. There is an extended time period based on a five-year lag, during which reproduction has already occurred, and yet no information is available from the fishery about how successful reproduction has been. And yet it is that very reproductive success that drives the productivity of the fishery. For the last eight years I have been involved in a program at the Tiburon laboratory that is designed to study rockfish recruitment and to improve management of these types of fisheries. The objectives of the rockfish recruitment program are, first and foremost, to develop indices of rockfish reproductive success that allow prediction of fisheries recruitment from information collected during mid-water trawl surveys of young-of-the-year. For those who don't know, young-of-the-year are fish that have yet to reach the first anniversary of their birthday. At a secondary level, we would like to improve our understanding of those factors that affect the establishment of year-class strength in these rockfishes. In other words, why do we see these large recruitment variations that we do, that drive the productivity in the fishery? And lastly, at the most general level, we wish to contribute to the overall scientific knowledge of the central California continental shelf and slope ecosystem, and to fisheries oceanography in general. And it's in this area, as well as the second, that I feel we can contribute to the goals of this symposium.
We've conducted our surveys aboard a NOAA fisheries research vessel, the David Star Jordan, which is ported in San Diego [Figure 3]. These surveys have been conducted every year since 1983 to the present. We'll be going out again this year. There are some serious funding questions about these fisheries research vessels, with the ongoing budget battles in Congress, but we won't get into that. Our surveys are conducted during May and June. We tow a large mid-water trawl that samples a swath of approximately 100 square meters and we sample young-of-the-year rockfish using this device.Our trawls are all done at night. This next graphic taken from Moser's work illustrates the ontogenetic sequence of developmental stages in Sebastes, which are somewhat unusual [Figure4]