You are here:
STABLE ISOTOPE STUDIES ON THE USE OF MARINE-DERIVED NUTRIENTS BY COHO SALMON JUVENILES IN THE OREGON COAST RANGE
Citation:
CHURCH, M., J. L. EBERSOLE, P. J. WIGINGTON JR, AND K. M. RENSMEYER. STABLE ISOTOPE STUDIES ON THE USE OF MARINE-DERIVED NUTRIENTS BY COHO SALMON JUVENILES IN THE OREGON COAST RANGE. Presented at 5th International Conference on Applications of Stable Isotope Techniques to Ecological Studies, Belfast, Northern Ireland, IRELAND, August 13 - 18, 2006.
Description:
Greatly reduced spawning runs of anadromous salmon in streams of the Pacific Northwest (USA) have led to concerns about the effects of reduced marine derived nutrients (MDN's) on sustaining over-wintering juvenile salmon in those streams. In response to these concerns, state and volunteer organizations have placed many thousands of hatchery-supplied salmon carcasses in streams to supplement nutrient sources. Almost no research has accompanied these management programs.
We are using stable isotopes (13C, 15N, 34S) to study the potential use of naturally-occurring salmon carcasses, eggs and resulting fry by over-wintering coho salmon juveniles in two streams of the Oregon Coast Range. Our work is paired with detailed data gathering on stream habitat condition, temperature, chemistry and PIT-tagging studies to monitor movement and growth. We have sampled two cohorts of coho over their stream residencies from eggs to smolts, with particular emphasis on critical life stages (e.g., eggs, emergence from gravel, initial growth, late summer feeding stress, winter feeding, and smolting).
The transition from egg to late-summer parr serves as an uncontrolled diet-switch. During this period isotopic signatures decrease from equilibrium at an enriched state due to higher trophic oceanic feeding (e.g., white muscle δ15N=17), to equilibrium (white muscle δ15N=6) with in-stream diets. One year with high winter spawner returns (and thus higher numbers of carcasses, eggs and fry) was associated with pre-smolts and smolts that showed not only δ15N elevated above late summer equilibrium but also wide scatter in δ15N (from 4 to 8), approximating a shift within the cohort equivalent to one trophic level. These results hint that some fish are consuming significant amounts of MDN's while others concurrently shift to lower signature diets. The year with much lower spawner returns did not show such patterns.
To help resolve questions of potential rapid and short term diet switching from lower signature in-stream or terrestrial food sources to higher signature MDN's during the winter period, we are experimenting with analyzing a very rapid turnover (hours/days) "tissue" fraction of the fish - mucus. To our knowledge, we are the first to perform stable isotope analyses of fish mucus. Sampling procedures (including non-lethal) have been developed and isotopic analyses are ongoing. We will compare this sampling with concurrent non-lethal sampling of caudal fins of the same fish to provide contrasting and complementary information on both longer-term slower turnover pools (fins) and much faster turnover fractions (mucus) to discern abrupt and fine time-scale diet switching to marine derived sources of nutrition.