I spent the past week at the 42nd Annual Larval Fish Conference in Victoria, BC. There were so many different kinds of research approaches to improve our understanding of larval fish ecology. This is the principal advantage of these small conferences: many of us have the detailed background knowledge of the most important problems, but usually we lack expertise in the application of several techniques and approaches to these problems within different species groups and ecosystems. The presentations I attended and conversations afterwards certainly led me to think differently about the approaches we take in both the lab and field.
The conference got off to a great start with the opening plenary session by Janet Duffy-Anderson – one of the leaders at NOAA in their application of environmental and larval fish data to ecosystem-level questions about fisheries productivity. She was a perfect fit for opening speaker because everyone got a glimpse of all the different factors influencing the life history of fishes, and how these data can be applied to real-world problems (e.g., fisheries management, which encompasses a multi-billion-dollar global industry). She gave numerous examples of how important environmental data are in understanding shifts in fish abundances and predicted that these kinds of data will be increasingly important in fisheries management.
One of the most fascinating talks I saw was by a sensory biologist studying anchovy eye morphology. These fish can actually detect polarized light and at certain angles. This polarization sensitivity allows them to double their sighting distance (presumably to better locate prey). The researcher was able to document a change in their behavior under polarized vs non-polarized light conditions. The fish without polarized light tended to filter feed, while the ones under polarized light would target and strike at prey. Specifically, they tended to strike at a 45-degree pitch angle, which is optimal for utilizing their polarized light sensitivity. Interestingly, the anchovy larvae we have imaged in the northern Gulf of Mexico have a consistent pitch angle of ~45 degrees. I think there is a lot of potential for using imaging to quantify behaviors in the field and coupling those observations with lab experiments using sensory biology to explain the behaviors. The details of the eyes, and the difference among species and families, may have a big influence in the behaviors of visually-oriented predators such as larval fishes.
There were also quite a few experimental talks examining the feeding rates and predator-prey dynamics of larvae using imaging. One even suggested that because early stage larvae were so clumsy at catching copepods that many larvae should be starving. This goes against evidence from net studies showing that most larvae are feeding successfully (they have full stomachs). However, at smaller sizes there could be large portions of the population that are starving, slow, and ultimately succumb to predation. This then begs the question – how do any larvae survive at all? One of the unanswered questions that many research groups are addressing is what conditions lead to successful first feeding (when the larvae go from yolk-sac to exogenous feeding) and fast growth? It could be environmental conditions (temperature, turbulence, etc.), the quality of their food, or a combination of factors.
After the conference I got a chance to go on a whale watch. We must have seen 15-20 orcas. Good thing I brought my camera!