New Page 2

RELATIVE IMPORTANCE OF POCS OIL PLATFORMS ON THE POPULATION DYNAMICS OF TWO REEF FISHES IN THE EASTERN SANTA BARBARA CHANNEL

Principal Investigators: Hunter Lenihan and Andrew Brooks

Overview

As part of our research, we have complete laboratory and field preparations, to design and conduct fish population surveys at POCS Platform Gina and three reference sites on Santa Cruz Island, to tag and recapture fishes at each site over multiple months, to estimate egg production during the late winter-spring nesting season, and to measure recruitment in late spring-early summer. This work covers a large proportion of the field component of our study, although we are in the process of finishing recruitment sampling, conducting a final population survey, and designing and deploying a prey tethering study that will estimate site specific predation rates on our model fish, Coryphopterus nicholsii (blackeye goby). Data will provide the information necessary to model population and source-sink dynamics of our model species at POCS oil platform Gina and three natural rocky reefs in the Santa Barbara Channel.

Population abundance

We completed population surveys at all sites to provide a time series of population abundance of our model species, Coryphopterus nicholsii (blackeye goby). Our surveys were conducted in 2003 (June, July, August, and December) and 2004 (January and June). Data from surveys conducted in June and July 2003 indicate that population abundance varied among sites (Figure 1). We are currently conducting our final population survey at all sites. Coupled with our tagging studies, our population censuses of gobies provide information on immigration, emigration, and mortality rates.

Figure 1: Results of population censes of C. nocholsii at POCS Gina and three reference sites on Santa Cruz Island (Chief Reef, Potato Rock, Orizaba). Error bars are 95% confidence intervals.

Per capita growth and survival

We decided to focus our tagging/recapturing effort on C. nicholsii, the blackeye goby, due to its high abundance across all sites and the feasability of sampling. Fish were tagged, released and re-censused to estimate per capita survival and growth. We completed four months of tagging (September, October, November, and January) in which 1656 C. nicholsii were tagged (Figure 2A) and 673 were subsequently recaptured (Figure 2B). This 40.6% recovery rate is extremely high and will allow for an accurate and precise estimate of population source-sink dynamics.

Reproductive output

To estimate reproductive output, we collected and enumerated egg masses from POCS Gina (n = 15 egg masses) and the three Santa Cruz Island sites (n = 11 egg masses at each site) in late Winter-Spring 2004 (Figure 3). Eggs were first noticed in April and some males were still guarding nests in June. We found eggs to be very difficult to maintain alive in the laboratory, probably because males were not present to keep water circulating over the eggs and/or provide them with some developmentally essential chemical signal/cue.

Figure 3: Mean number of eggs per clutch for egg masses of C. nicholsii, which were collected from POCS Gina and the three reference sites on Santa Cruz Island. Error Bars are 95% confidence intervals. Note that the Potato Rock site was divided into a deep and midwater sampling scheme. For all Santa Cruz Island sites n = 11, including both depths at Potato Rock (total n at Potato Rock = 22). At Gina n = 15.

Recruitment

The recruitment of blackeye gobies was estimated at POCS Gina, and our three reference sites in March-July 2004. Recruits were quantified by divers who counted the total number of YOY recruits (fishes <1 cm in length) over four replicate 20 m x 2 m transects (40 m²) at each site. We found very few recruits in March – May, but we found an increasing trend in recruitment in June (Figure 4). We will also quantify recruitment in July and August because recruitment appears, at least this year, to be protracted over a substantially long period.

Figure 4: Recruitment at POCS Gina and three reference sites on Santa Cruz Island. Error bars are 95% confidence intervals.

Biotic interactions

The rate of predation on Coryphoterus by other fishes was be estimated in July and August 2004 by tethering gobies at each site and examining their survival over 24 hr periods. Gobies were tethered at different depths and in different microhabitats, features that distinguish POCS platforms and natural reefs in our study, to determine how these factors influence their survival.

Age and Growth, Connectivity

We collected otoliths from fishes at each site and are in the process of determining ages for fishes across a varied size range (Figure 5).

Figure 5: Length – Weight relationship for all specimens collected for otolith removal.

These data will provide the first age and growth characterization for this species. In addition, we are working with the Gaines and Warner laboratories, and the PISCO program at UCSB to identify micro-chemistry signatures from platform Gina and our natural reefs. These data will potentially provide information regarding the origin of individuals within populations at each site. This study will examine whether goby populations are well-mixed within the Santa Barbara Channel, or, in contrast, whether there is a degree of self-seeding on these spatially separated locations.

Educational opportunities

We involved six graduate and nine undergraduate students in our research during the fiscal year. We also had six staff personnel volunteer their time on our project. Our study overlapped with dissertation research being conducted by graduate student Stu Levenbach of the Department of Ecology, Evolution, and Marine Biology at UCSB. He was able to access his sampling sites and was provided a buddy diver to conduct his sampling and experiments in exchange for help with our sampling and tagging studies.