Juvenile Herring Growth and Habitats - [UNFORMATTED]

Description of umbrella "Juvenile Herring Growth and Habitats project":

Aerial surveys typically lack precision and are not sufficiently accurate to provide a standalone estimate of stock biomass (Krebs 1989; Gunderson 1993; Hunter and Chumside, 1995). Varia estimate of stock biomass (Krebs 1989; Gunderson 1993; Hunter and Chumside, 1995). Variability due to sighting conditions, changes in vertical distribution of fish schools, and surveyor bias largely go unmeasured (Hunter and Chumside, 1995). It is therefore important to standardizea s manys urveyp arameters,s ucha s aircraft speed, altitude, time of day, etc., that can affect aeriale stimates(Caughleye t al., 1976).Thus, the main purpose of this study was to develop methodology and improve the precision of visual aerial survey estimates of surface schooling forage fish distribution and abundance. The specific objectives were to: 1) develop an appropriate survey design incorporating estimation of detection error and surveyor bias and defining optimal survey constraints, 2) determine the accuracy of fish species and age class discrimination from visual aerial observations, 3) determine the repeatability of aerial measurements, and 4) determine the spatial resolution of aerial measurements needed to use the results in ecological analyses. A secondary objective was to develop abundance estimates for jellyfish aggregations (Aequorea sp.) and foraging sea birds. This study demonstrates that aerial surveys are a useful tool for ecological research of forage fish, sea birds, and other marine species. In addition, surveyors can discriminate forage fish species and produce repeatable results with an acceptable level of error. The methods described in this report outline an efficient, cost effective
way to obtain information on the distribution and abundance of forage fish and their predators. In addition, we have identified a model and the sources of error affecting the accuracy and precision of survey results. (from EVOSTC project #320-T final report)

***This work is part of a multi-reseracher, multi-project study of forage fish ecology and surving. The data here include tucker trawl larval surveys. Other data for this project can be referenced in the following packages: df35d.93.12 (http://evos.nceas.ucsb.edu/evos/metacat/df35d.93.12/default).

The hypothesis that juvenile herring aggregated within bays was tested by examining the relationship between the spatial distributions of herring and distances from shore. A group of data cells was considered to be a fish school if the sum of the differences between latitudes and longitudes of adjacent cells was >0.009'. Visual examination of the echograms and plots of cells along transects supported this assumption. Bays were statistically defined from passages or open coast line by creating a parameter that is the
sum of the three nearest shore distances (sum3NSD), each separated by 90". This measurement was calculated at 12 bays and along 2 passages, 26 inside bays and 17 outside bays, to verify that it accurately defined bays, passages, and open coast line. The sum3NSD for each herrin g school within each size mode was calculated and compared to the same measurements from randomly selected points along the transect for the three surveys usinga chi-squared test. Expected values were grouped according to Cochran's rule (Sokal & Rohlf 198 1). This technique corrected sampling and shoreline structure biases, for example 80 % of the shoreline may have been in bays or we may have surveyed bays more than open coastline or passages. Further to determine if there were physical differences in water mass and larval fish community structure at these locations vertical water profiles measuring temperature and salinity at 1 m intervals, using a SeaBird instrument, and two tucker trawl samples (1 m^2 mouth, 505 micronmeter mesh nets) were collected at each of these sites. Tucker trawl samples were preserved in 10% formalin for >48 h, then transferred to 50% isopropyl alcohol and sorted to species and measured in the laboratory.