Publikationer

A recent meta-analysis by Barneche et al. (Science 360(6389): 642) show that fish reproductive output scales hypergeometrically with female weight. This result challenges the common assumption that reproductive output is proportional to weight. The implication made is that current theory and practice severely underestimates the importance of larger females for population replenishment. Their example for cod shows that current practice makes an error of 149%. By properly accounting for fish demography we show that the error is maximally on the order of 10%, and in most other fish stocks likely much less.

Size at maturity in ectotherms commonly declines with warming. This near-universal phenomenon, formalised as the temperature-size rule, has been observed in over 80% of tested species, from bacteria to fish. The proximate cause has been attributed to the greater temperature dependence of development rate than growth rate, causing individuals to develop earlier but mature smaller in the warm. However, few studies have examined the ontogenetic progression of the temperature–size response at high resolution. Using marine planktonic copepods, we experimentally determined the progression of the temperature-size response over ontogeny. Temperature-size responses were not generated gradually from egg to adult, contrary to the predictions of a naïve model in which development rate was assumed to be more temperature-dependent than growth rate, and the difference in the temperature dependence of these two rates remained constant over ontogeny. Instead, the ontogenetic progression of the temperature-size response in experimental animals was highly episodic, indicating rapid changes in the extent to which growth and development rates are thermally decoupled. The strongest temperature-size responses occurred temporally mid-way through ontogeny, corresponding with the point at which individuals reached between ~5–25% of their adult mass. Using the copepod Oithona nana, we show that the temperature-dependence of growth rate varied substantially throughout ontogeny, whereas the temperature dependence of development rate remained constant. The temperature-dependence of growth rate even exceeded that of development rate in some life stages, leading to a weakening of the temperature-size response. Our analyses of arthropod temperature–size responses from the literature, including crustaceans and insects, support these conclusions more broadly. Overall, our findings provide a better understanding of how the temperature-size rule is produced over ontogeny. Whereas we find support for the generality of developmental rate isomorphy in arthropods (shared temperature dependence of development rate across life stages), this concept should not apply to growth rates

We present a statistical method for intercalibration of fishery surveys methods, i.e. determining the difference in catchability and size selectivity
of two methods, such as trawl gears or vessels, based on data from paired fishing operations. The model estimates the selectivity ratios in
each length class by modelling the size distribution of the underlying population at each station and the size-structured clustering of fish at
small temporal and spatial scales. The model allows for overdispersion and correlation between catch counts in neighbouring size classes. This
is obtained by assuming Poisson-distributed catch numbers conditional on unobserved log-Gaussian variables, i.e. the catch is modelled using
log-Gaussian Cox processes. We apply the method to catches of hake (Merluccius paradoxus and M. capensis) in 341 paired trawl hauls performed
by two different vessels, viz. the RV Dr Fridtjof Nansen and the FV Blue Sea, operating off the coast of Namibia. The results demonstrate
that it is feasible to estimate the selectivity ratio in each size class, and to test statistically the hypothesis that the selectivity is
independent of size or species. For the specific case, we find that differences between size classes and species are statistically significant

Choanoflagellates are unicellular eukaryotes that are ubiquitous in aquatic habitats. They have a single flagellum that creates a flow toward a collar filter composed of filter strands that extend from the cell. In one common group, the loricate choanoflagellates, the cell is suspended in an elaborate basket-like structure, the lorica, the function of which remains unknown. Here, we use Computational Fluid Dynamics to explore the possible hydrodynamic function of the lorica. We use the choanoflagellate Diaphaoneca grandis as a model organism. It has been hypothesized that the function of the lorica is to prevent refiltration (flow recirculation) and to increase the drag and, hence, increase the feeding rate and reduce the swimming speed. We find no support for these hypotheses. On the contrary, motile prey are encountered at a much lower rate by the loricate organism. The presence of the lorica does not affect the average swimming speed, but it suppresses the lateral motion and rotation of the cell. Without the lorica, the cell jiggles from side to side while swimming. The unsteady flow generated by the beating flagellum causes reversed flow through the collar filter that may wash away captured prey while it is being transported to the cell body for engulfment. The lorica substantially decreases such flow, hence it potentially increases the capture efficiency. This may be the main adaptive value of the lorica.