Recovery of severely declining resource stocks often leads to enforced quotas or reduced human access to those resources. Predators, however, do not recognize such restrictions and may be attracted to areas of increased prey abundances where human extraction is being limited. Such targeting by predators may reduce or retard the potential recovery of depressed stocks. In the San Juan Islands, northern Puget Sound, USA, marine reserves were implemented to recover depressed fish populations. We examine the role of harbor seals Phoca vitulina in the San Juan Islands food web. We describe the temporal and spatial variability in their diet, emphasizing species for which reserves were established (rockfish Sebastes spp.) and other important depressed stocks, including salmon Oncorhynchus spp. and Pacific herring Clupea pallasii. During winter and spring, seals primarily consumed Pacific herring, Pacific sand lance Ammodytes hexapterus, northern anchovy Engraulis mordax, and walleye pollock Theragra chalcogramma. During summer/fall, adult salmonids composed >50% of the diet and were particularly important in odd-numbered calendar years, when pink salmon O. gorbuscha spawn. Rockfish were not a primary prey species at any time of the year, suggesting that the abundance of alternative prey species may reduce predation pressure and provide a critical buffer to rockfish predation. The importance of considering increased visitation by marine predators to areas where potential prey are enhanced through restrictions on human extractions should be considered when modeling the efficacy of quotas and reduced access areas, such as marine reserves.
Project status: A peer-review article has been published. (5/2014)
SeaDoc funded a River Otter diet and predation study by Monique Lance of the Washington Department of Fish & Wildlife.
The study aims to describe the diet of river otters and investigate the potential effect they have on rockfish and salmon populations in the San Juan Islands.
Rockfish and salmon are currently listed under the Federal Endangered Species Act. Because of the dramatic decline in these species over the past several decades, Marine Protected Areas have been created to assist in their recovery.
However, little attention has been paid to how predators respond to increased prey densities. Therefore it’s important to investigate the diet of potential predators.
Otter scat samples were collected in the spring, summer and fall of 2008 on Fidalgo, San Juan and Orcas Islands. The scat samples were cleaned and invertebrates in them have been identified in a previous project. This project now allows for the analysis of fish remains in the scat, as well as examinations of spatial variation among the project sites and temporal variations through 2008. Data will be compared to diet data from Alaska and British Columbia, and also to the diet of various other predators, including harbor seals and Steller sea lions.
Photo by Michael Ransburg: Creative Commons license.
This entertaining video shows how you can release bloated rockfish to give them a chance at survival. Rockfish are long-lived fish (many live to 100 years or more!) found in the Northeast Pacific ocean. Seven species are considered overfished and several states require these species to be discarded if captured. However throwing these fish overboard often leads to their demise because of pressure-related injuries called barotrauma. Find out why a rockfish gets barotrauma and how to use a variety of recompression devices to help rockfish return to their depth of capture. Have a heart, do your part, and send them back down…
NOAA recently published the proceedings of the Rockfish Recovery Workshop we helped host in 2011. It’s 124 pages of state of the art science on the status, history and future of rockfish populations, many of which are way down from historic levels and several of which are listed on the Endangered Species List.
Download the PDF here: Rockfish Recovery Workshop Proceedings
Rockfish are pretty amazing. Some live up to 200 years. Others will find their way back to their rock-pile homes if you transport them to another spot miles away.
SeaDoc’s role in sponsoring the workshop is a good example of how we’re able to bring our whole-ecosystem perspective to the table. Obviously rockfish recovery has to take place on both sides of the international border. But things quickly become complicated when you’re talking about scientists traveling over the border to attend a workshop. Canadian scientists couldn’t get travel money from their agencies. NOAA and the Washington Department of Fish & Wildlife, being US government organizations, couldn’t pay for the travel of foreign nationals. But SeaDoc could. Because we’re funded mostly by private donations, we can spend money in ways government organizations can’t. So we sponsored a couple of high-ranking scientists from British Columbia to come down and share their experiences and perspectives.
SeaDoc has done numerous projects on rockfish over the years.
- SeaDoc’s mapping lab partner, Tombolo, led by Gary Green, Ph.D, has been instrumental in mapping rockfish habitat in the Salish Sea over the past decade. You can see rockfish habitat in our recent Maps of the Month in our November 2012 and January 2013 newsletters.
- We’ve sampled harbor seal scat to find out whether they are eating depressed rockfish stocks: http://www.seadocsociety.org/node/377
- Genetic identification of brown rockfish stocks: http://www.seadocsociety.org/node/216
- Analyzed otoliths (ear bones) to understand population structures of quillback rockfish: http://www.seadocsociety.org/node/498
- Studied whether river otter predation is affecting rockfish: http://www.seadocsociety.org/river-otter-diet-project
- Investigated whether Marine Protected Areas are effective for rockfish recovery: http://www.seadocsociety.org/rockfish-mpa-research
- Trained recreational divers to collect data on fish populations: http://www.seadocsociety.org/node/84
Watch our 2011 marine science lecture on rockfish here: http://www.seadocsociety.org/node/653