Hennen, D., Jacobson, L., and Tang, J. 2012. Accuracy of the Patch model used to estimate density and capture efficiency in depletion experiments for sessile invertebrates and fish. – ICES Journal of Marine Science, 69: 240–249. The Patch model is used to analyse depletion experiment data for sessile invertebrates and fish that do not randomize after sampling. Simulations indicate that density and capture efficiency estimates were useful under realistic conditions for Atlantic surfclam (Spisula solidissima) and many other sessile demersal species. Density estimates were generally biased low by position-data errors, whereas efficiency estimates were relatively unbiased. A new “hit” matrix method improved the accuracy of efficiency estimates, reduced the variability for efficiency and density estimates, and simplified assumptions about the movement of organisms after sampling. Depletion tows should be spaced to cover the entire study area and to intersect in areas where densities are not low. Model estimates can be made for individuals fully or partially selected by the sampling gear, and information about size selectivity is useful. Patch-model estimates can be used to calculate swept-area abundance or biomass, estimate catchability coefficients for survey or catch per unit effort data, form prior distributions used in stock assessment models, and estimate efficiency for other types of sampling gear.
Solar zenith angles are useful in diel studies because they are directly related to potential solar irradiance at the point of sampling and can be calculated from location, date, and time of day. We used zenith angles to quantify diel vertical migration effects on both the probability of a positive tow and catch size for longfin squid (Doryteuthis pealeii) using two-stage generalized additive models (GAMs). Zenith angles were better than time of day for modeling diel effects on inshore longfin squid bottom trawl survey catches and were particularly suitable for data collected over large areas and extended time periods. Diel effects were size-specific in most cases. Our expected catch method can be used to account for diel effects when estimating swept-area stock size from research survey data. Differences in observed day–night catches and model results show the potential for bias in swept-area stock size estimates that ignore diel migration effects. Zenith angles may be useful in specifying prior distributions for survey catchability parameters in stock assessment models.
The maximum sustained swimming speeds (Ums) for large (0.45 m long) and small (0.15 m) Atlantic salmon were respectively 0.91ms−1 and 0.54ms−1. Video and cin6 films of fish swimming close to Ums were analysed to obtain variables required for the application of two hydrodynamic models, those of Lighthill and Yates, to determine the mean thrust (T) and mean power output (P) at these swimming speeds (U) close to Ums. A large fish (‘Salmon’) and a small fish (‘Smolt’) were selected for analysis. For salmon using Lighthill's model, T=0.30N and P=0.26W, and using Yates' model, T=0.28N and P=0.25W (U/=0.87ms−1=0.96Ums). For smolt using Lighthill's model, T=0.0052N and P=0.0019W, and using Yates' model, T=0.0065 N and P=0.0024W (U=0.37ms−1=0.69Ums). The power output for smolt swimming at 0.69Ums was corrected to that required to swim at Ums, giving P=0.0059W (Lighthill's model) and P=0.0074W (Yates' model).
At Ums it was assumed that all the red muscle was used. Two fish were selected from each size group and cross-sectioned to estimate their red muscle masses. Using a maximum mass-specific power output of 5–8 W kg− for slow red muscle fibres allowed us to calculate that the large and small fish have a power output capacity of 0.125–0.3 W and 0.007–0.019 W, respectively.
The power output values at Ums derived from the different approaches for the large (0.25–0.26 W) and small (0.0059–0.0074 W) salmon agree closely. Effects of scaling are discussed.
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