Monterey Bay Salmon & Trout Project

Update on NOAA Fisheries Research & Monitoring of Scott Creek Salmonids
By Sean Hayes

As many of you know, several of us from NOAA’s Southwest Fisheries Science Center in Santa Cruz began conducting research on Scott Creek salmonids in January 2002. Over time, the scope has expanded along with new members to the team, so let me just review what we have going on and who is doing it. I continue to oversee operations of the adult and juvenile traps on Scott Creek, which in turn generates data for many of the following projects. Morgan Bond completed his master’s thesis last spring on the effects of estuarine rearing on juvenile steelhead and marine survival.

He found that 85% of the returning adult steelhead in Scott Creek are those that reared in the estuary during the summer lagoon period when a sandbar forms and isolates the estuary from the sea. Morgan’s research indicates that the estuary is a valuable habitat for the fish and it is critical that it not be breached during summer months so that the fish have a place to grow. We recently completed a companion study on this subject showing that growth of fish in the estuary is much faster than in the upper watershed. Morgan also found juvenile steelhead need to be larger than approximately 150mm in length (~6 inches) when they enter the ocean in central California to have a chance of surviving to adulthood, and of course it was predominately the estuary- reared fish that achieved these minimum sizes.

It’s a little early to tell, but based on data from adult counts we are getting at the weir, it looks like the number of returning wild adult steelhead is closely related to the number of fish that rear in the estuary each summer. This raised the question for us of what are steelhead doing in streams along the central coast without estuaries? Chad Hanson decided to pursue this question for his master’s thesis and compared Scott and Waddell Creeks (streams with estuaries) to San Vicente and Big Creeks (on Big Sur coast), two streams without estuaries.

Chad is finishing his thesis now and we are awaiting the final conclusions, but the preliminary data suggest that in watersheds without estuaries, fish are forced to rear in the upper watershed and migrate downstream as older large mature smolts, which can be difficult in streams with limited growth opportunities in the upper watershed. We suspect that these watersheds may not be able to support as many steelhead, but require more data to be sure of this point – in either case it points to the need to protect and preserve our local estuary habitat for steelhead populations on the central coast. On the question of marine survival, we recently gained some insight into what happens to some of the fish that we never see again when they leave the river.

This fall we discovered many of our tags on Año Nuevo Island. These were from fish that were tagged in Scott, Waddell, Gazos and Soquel Creeks. It appears that one of the animals that lives on Año is eating juvenile salmon. We are not sure which animal yet, but are suspicious that it is Western gulls! We have continued our research on steelhead genetics as well, investigating questions related to resident versus anadromous behavior in local steelhead – particularly in Scott Creek. Devon Pearse has been working on analyzing DNA samples we collected from fish in Scott Creek. Briefly, it appears that there are distinct genetic populations of “rainbow trout” above all the waterfalls in Scott Creek that serve as barriers to steelhead.

However each of these populations appears to be closely related to the steelhead in Scott Creek and were probably introduced/planted above the waterfalls by humans some time in the last 100 years or so. Some of these fish continue to come down over the waterfalls and it appears that they may be breeding below the waterfalls in the steelhead habitat. It is unclear at this point how much breeding is taking place between the steelhead and resident populations, and we are hoping to conduct more research in this area.

Another one of the researchers at the lab, Sue Sogard, is doing some work comparing steelhead from the Central Valley populations to local populations in Scott and Soquel creeks. She has two people working with her on this – Dave Swank – who came to us from Michigan where he did his graduate school research on steelhead in the Great Lakes, and Mike Beakes, who has worked on several west coast salmon projects. This project has been underway for less than a year and is just starting to get some interesting results. Wait until the next newsletter for details!

Finally – the last of the steelhead projects – Jeff Harding is studying diet differences for fish feeding in the estuary and upper watershed to see if there are differences in types of food available. The preliminary results are that the estuary diet is composed primarily of amphipods and that there are a lot of them in comparison to the upper watershed where diets are more traditional aquatic and terrestrial insects (stone, may and caddis flies), which are somewhat less abundant. Alison Collins and Morgan Bond are working to understand why this is by trying to assess whether marine nutrients (from sources like rotting kelp) are having significant contributions to the estuary food web.

Moving on to coho salmon – we have been mostly monitoring population dynamics and habitat use. The coho appear to be less dependant upon the estuary for juvenile rearing. We suspect this is because it is too warm for them during the summer or possibly due to competition issues with steelhead. In either case the coho are spending one to two years in the creek before going to sea. This is new information – until a few year ago, it was felt coho primarily went to sea after only one year in freshwater in central California. Thanks to our PIT tagging efforts of juvenile coho and scale analysis by us and Jerry Smith at San Jose State, we now know that in years when there are a lot of juvenile coho in the watershed, some tend to spend an extra year rearing in the watershed to compensate for competition between juveniles during the high density years. This has contributed to the reestablishment of some weak coho year classes.

In 2002 – we had a great return and there were so many juveniles in the creek that some stayed an extra year until 2003, which had a horrible adult return – probably less than 10 adults. So in 2004 when the smolts from 2003 were going to sea, there were a few extra fish held over from 2002. Therefore, last year, 2006, when the juveniles from 2003 were supposed to return we had about 50 adults instead of 10. Still low numbers, but a step in the right direction. In addition, the collaborative effort between MBSTP and NOAA to maintain a coho captive broodstock program started to bear results. Using the weir, we were able to collect a couple wild fish for the hatchery, and at the same time there was some successful spawning of the captive broodstock. As a result there were over 2000 extra smolts to be released this spring for the first time ever in this weak year class. A sad turn of events happened this year, with the lack of rain in January.

Unfortunately, coho salmon were not able to get into the creek and as a result what was expected to be a return of well over 100 fish, ended with only a few fish coming back. We counted FOUR and based on surveys and the weir data, expect there weren’t many more than that. This raises concern about long- term trends for coho in the area if we are headed into an extended drought period again. The good news is that once again thanks to collaborative efforts of MBSTP and NOAA, we were able to collect a couple of wild fish with the weir and these were spawned along with captive broodstock fish raised by Dave Streig (MBSTP) and Erick Sturm (NOAA) and it looks like there could be over 3000 smolts to release next spring which could result in the return of as many as 90 adults in 2010 when this year class is scheduled to return!

Back