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The Problem
The protection of water quality in Abbotts Lagoon and its associated flora and fauna are of great concern to the NPS. Adverse effects from permitted uses such as dairy and beef ranching, and the listing of numerous plant species as threatened or endangered, have raised serious concerns over the health of the lagoon. Within the past two years, algal blooms have been reported in the lagoon. In 1989, a USGS study determined that the lagoon received considerable quantities of nutrients (nitrates and phosphates) through nonpoint source pollution, especially from ranching operations in the watershed. High nutrient concentrations in lagoon water could potentially stimulate excessive aquatic plant growth and increase the overall biochemical oxygen demand, thereby creating stressful hypoxic conditions that adversely affect fish. Very little is known about fish populations inhabiting Abbotts Lagoon and the environmental conditions that influence their abundance and distribution. Surveys conducted in 1984 by Point Reyes National Seashore (PORE) revealed populations of Sacramento perch (Archoplites interruptus) and Pacific herring (Clupea pallasi). However, underwater observations made by scuba diving during the USGS study in 1989 yielded ...very few organisms living in the lagoon other than arthropods and microorganisms. Moreover, the lagoon ...lacked significant numbers of bivalves or other filter feeders. It is unknown if the seeming absence of fishes in 1989 was a result of the cursory nature of underwater observations or if water quality conditions had become unsuitable for fish life. On March 26, 2002, this sub-task was modified to include a new study of the trophic ecology of Sacramento perch inhabiting Abbotts Lagoon. The new study consists of two parts: a field investigation and a laboratory investigation. This subtask is funded under reimbursable agreement number 4706-48510 (Project Proposal No. CA99c) with the USGS-Water Resources Division and the BRD. Objectives Protection of water quality in Abbotts Lagoon: Specific objectives of this investigation were to (a) inventory the fish species inhabiting Abbotts Lagoon, (b) determine if spatial distribution and relative abundance of fishes vary seasonally, and (c) relate the distribution patterns of fishes to variations in water quality or other environmental conditions in the lagoon. In addition, collaborative work by the USGS Water Resources Division will compare water quality of storm runoff from subbasins with contrasting lands uses, and evaluate seasonal variations in water quality in a perennial tributary stream and the lagoon. Trophic ecology of Sacramento perch:
This investigation was intended to characterize gut contents of various age classes of Sacramento perch over a one-year period and document weight, length, condition factor, sex, and age-and-growth (from scale analysis) of perch. In addition, this investigation collected data for constructing a bioenergetics model of Sacramento perch, including measurements of maximum and optimum respiration and consumption at various water temperatures. By documenting the relation between fish diet and subsequent growth, and how energy consumed is allocated, we hoped to develop a better understanding of the ecological role of Sacramento perch in the aquatic food web and energy flow pathway of Abbotts Lagoon. Methodology Protection of water quality in Abbotts Lagoon: Intensive fishery surveys were conducted seasonally (spring, summer, fall, winter) from a minimum of one reach in the upper lagoon (farthest from the ocean), three reaches in the middle lagoon, and three reaches in the lower lagoon (adjacent to the ocean). The specific location of each sampling reach was randomly selected, and included a near-shore site and an off-shore site. Each site was fished overnight (approximately 4:00 PM to 8:00 AM; the actual fishing time was recorded) with a single 125-ft-long by 8-ft-deep floating variable-mesh (experimental) monofilament gill net containing 25-ft panels of the following bar-mesh sizes (in inches): 1/2, 1, 1-1/2, 2, and 2-1/2. Grab measurements of water quality (temperature, dissolved oxygen, pH, salinity, turbidity) was also recorded at each site by taking a vertical profile (1.0-m intervals) at the start and end of each gill net set. Fish caught with gill nets were identified to species, weighed (to nearest 0.1 g) and measured (standard length to nearest 1 mm), then released in the vicinity of capture. Small-mesh (1/8-inch to 1/4-inch) dipnets, throw nets, and beach seines were used in wadable portions of the lagoon to supplement the gill net catch of small fish species. However, unlike gill net catches, fishing effort for dipnetting, thrownetting, and seining was not standardized, and captured fish were not weighed or measured (just identified and counted, then released alive in the vicinity of capture). Trophic ecology of Sacramento perch:
Fish were collected with floating gill nets at seasonal (once every three months) intervals beginning in March 2001 and ending in February 2002. A random sample of 10 Sacramento perch from each age class (as determined by Aceituno and Vanicek 1976) were selected for scale collections and diet analysis. At the same time, water quality readings were taken at 1-meter intervals from surface to bottom using a Hydrolab DataSondeŽ3 multiprobe and SurveyorŽ4. Samples of gut contents for diet analysis were collected from the same fish used to obtain scales. Gut contents were removed with a stomach pump. Upon removal, gut contents were bottled, labeled, and preserved in 10% formalin for later measurement and identification. Gut contents were identified to an appropriate taxonomic level and quantitatively described according to percent composition, percent by number, and percent wet weight. Prey biomass was determined from direct measurements or estimated from length-mass relationships. The mass of prey organisms were then converted to calories per gram wet mass for use in the bioenergetics model. Fifty perch were collected in May 2001 for bioenergetics modeling. Ten fish were acclimated to five different temperatures ranging from 5°C to 25°C for one week. Procedures for measuring respiration followed Jobling (1994). Fish were fasted for 48 -72 hours prior to introduction into the respirometry chamber to eliminate effects from previously eaten foods. Fish were allowed to acclimate overnight in the respiration chamber before measuring metabolic rate (respiration measured over a time period of 8-12 hours or longer). These same fish were used for determination of maximum and optimum food consumption rates at selected temperatures. Food consumption will be estimated from the maximum daily ration of that fish at a particular mass and temperature. Fish were fed ad libitum to estimate maximum daily consumption rate. Consumption data and respirometry data, along with caloric content of prey derived from diet, will be inputted into the Fish Bioenergetics 3.0 model. Highlights and Key Findings Protection of water quality in Abbotts Lagoon:
The purpose of this study was to gain a better understanding of fishery resources in Abbotts Lagoon, Point Reyes National Seashore. During February/March, May, August, and November 1999, fish were sampled with gill nets and minnow traps from as many as 14 sites in the lagoon. Selected environmental variables--temperature, dissolved oxygen, pH, total ammonia (NH3 + NH4+), salinity, turbidity, water depth, and bottom substrate composition--were also measured at each site. A total of 2,656 fish represented by eight species was captured during the study. Gill nets captured Sacramento perch, largemouth bass (Micropterus salmoides), Pacific herring, prickly sculpin (Cottus asper), silver surfperch (Hyperprosopon ellipticum), longfin smelt (Spirinchus thaleichthys), and striped bass (Morone saxatilis), whereas minnow traps captured Sacramento perch, prickly sculpin, and threespine stickleback (Gasterosteus aculeatus). Cluster analysis (Wards minimum variance method) of fish catch statistics identified two major species assemblages--the first dominated by Sacramento perch and, to a lesser extent, by largemouth bass, and the second dominated by Pacific herring and threespine stickleback. Simple discriminant analysis of environmental variables indicated that salinity contributed the most towards separating the two assemblages. These findings support the generally accepted view that fish species assemblages in estuarine habitats are structured primarily by the tolerance of individual species to salinity gradients. However, other investigators reported that Sacramento perch, threespine stickleback, and possibly Pacific herring can easily tolerate the range of salinities (fresh to brackish waters) encountered during this study. Although beyond the scope of this study, food availability, predation pressure, or other ecological factors influenced by the salinity gradient could ultimately prove to be most responsible for structuring fish species assemblages in Abbotts Lagoon. Trophic ecology of Sacramento perch: Fieldwork by a graduate student from Humboldt State University began in April 2001 with a preliminary sampling trip to Abbotts Lagoon to gain experience with various gears and procedures. Sampling trips were made in June, July, and November 2001, and in January 2002. Altogether, about 300 Sacramento perch have been captured. In addition to weighing and measuring Sacramento perch and collecting their gut contents by using a stomach pumping technique, some perch were transported alive to hatchery facilities at HSU for use in bioenergetics experiments. The bioenergetics experiments began in August and continued through November 2001 with six perch acclimated to 10°C, 20°C, and 24°C. Maximum food consumption was determined in these fish over a 24-hr period. In January 2002, an additional 35 perch captured from Abbotts Lagoon were transported to HSU, but all succumbed to an Ich outbreak and other unknown causes. Consequently, the six perch used in earlier bioenergetics experiments were once again used for feeding trials and measurements of metabolism. This time, perch were acclimated to 11°C, 17°C, and 22°C, respiration was measured over a one-hr time period, and maximum food consumption was measured over a 24-hr period. These data are currently being used to estimate optimum temperatures for both metabolism and feeding. Future work (currently scheduled for completion in March 2002) will involve acclimating perch to 9°C and 13°C before taking respiration and feeding measurements. In addition, field trips to Abbotts Lagoon are scheduled for April and June 2002 to gather additional data on gut contents and to collect additional test specimens for use in bioenergetics experiments. Analysis of gut contents and aging of fish scales, plus construction of the bioenergetics model, are expected to begin in April 2002. Where Are We Headed In 2003 Write-up of a Master's degree thesis on Sacramento perch bioenergetics is expected to occur during FY-03. Project Contact Michael Saiki Email: mike_saiki@usgs.gov Publications |
