Optimal time and sample allocation for unicohort fish larvae, sea-spawning whitefish (Coregonus lavaretus s. l.) as a case study

• The spatio-temporal variation in sea-spawning whitefish (Coregonus lavaretus s. l.) larval densities and their sizes was analysed with the aim to suggest a useful sampling dimensioning in terms of number of replicates and to find an optimum time for sampling to minimize the sampling variance. We also investigated the potential to predict optimal sampling in advance based on air temperature. The larval data used in the study were collected in the northernmost part of the Baltic Sea during 1979-2011. The analyses of the optimum time for sampling showed a sharp peak associated with a huge variation in density for larvae sizes similar to 15 mm length. Larvae sizes in the range 20-30 mm had intermediate densities with relatively low variance, while the densities of larger larvae declined with an increase in the relative precision. The 20-30 mm range was identified as a reliable size window for sampling, and the best predictor of larvae size was the temperature sum, using offshore air temperatures starting at 26 April. The between-year variance of the larvae mean sizes in the size range 20-30 mm was on the average 64% higher for fixed date sampling compared with fixed temperature sum sampling. The optimum sampling time was identified to the date when reaching 270 degrees C d for the southern, and 335 degrees C d for the northern locations. These temperature sums were generally reached in the first 2 weeks of June, but some years as late as the last week in June. Confidence intervals from a negative binomial distribution should be used rather than intervals based on the normal distribution due to the skewed sampling distributions. Bootstrap analyses showed that 10-30 replicates may give sufficient precision to detect significant changes in sea-spawning whitefish larval densities. Revisiting the same areas during the larval growth season (time window) did not improve the precision significantly.

Subject headings

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Fisk- och akvakulturforskning (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Fish and Aquacultural Science (hsv//eng)

Publication and Content Type

ref (subject category)

art (subject category)