Lorenz Hauser Research

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Finding Nemo in Puget Sound

A multidisciplinary approach to estimating larval dispersal rates and distances in Puget Sound brown rockfish (Sebastes auriculatus)

Lorenz Hauser (UW Fisheries), Mitsuhiro Kawase (UW Oceanography),
Ray Buckley (WDFW, UW Fisheries), Larry LeClair (WDFW), Mari Kuroki (University of Tokyo)

 

Nemo

Nemo in Puget Sound?

In the movie, clownfish Marlin swam oceans, battled sharks and rode currents to find his son Nemo after he lost him on the reef. We are trying to do the same here: every year, baby rockfish born in Puget Sound are washed away, and nobody knows what happens to them or where they end up. We don't want to battle sharks and swim oceans, so we are using a combination modern scientific techniques to find Nemo and to work out where he went and how he got there.

 

Background: Why find Nemo?

Marine Protected Areas (MPAs) are one of the main tools for maintaining fish populations and conserving biodiversity. We know already that closing fisheries in specific areas may lead to more fish, larger fish and a more diverse community. There are also reports that such benefits 'spill over' to adjacent areas, mainly by emigration of adult fish, thus benefitting fisheries and biodiversity in general. What we absolutely don't know is the effect of MPAs on the production of new fish (called 'recruitment'), especially how far fish in a specific MPA would spread their offspring and if they have any chance to reach the next MPA. Most species of marine fish and invertebrates have a pelagic phase, when larvae float in the water column and are potentially carried away by ocean currents. These larvae are tiny, and so what we usually observe is that they hatch and, several weeks or months later, juveniles appear. Given the length of this pelagic phase, fairly strong ocean currents and the lack of any barriers that could stop the larvae, such 'dispersal' can be extensive. Nemo may go a far, far way!

As there are no clownfish in Puget Sound, we are working on another species, brown rockfish (Sebastes auriculatus). Adult brown rockfish live in rocky reefs in Puget Sound and generally don't move much. In late summer, females give birth to tens of 1000s of live larvae which then drift around for about two months before they settle to the bottom as juveniles. We will use three techniques (oceanographic models, genetics, otolith microstructure to track larvae that are born on a reef at Point Heyer, Vason Island, Puget Sound.

brown rockfish
Brown rockfish (Sebastes auriculatus). Photo by Jay Orr, Alaska Fisheries Science Center, NOAA.

Larry diving
Larry LeClair taking a break from sampling

Oceanography

Grab the shell, dude, but no hurling....

The aim of the oceanographic part of this project is to predict the dispersal of larval rockfish as passive particles. While we know that larval rockfish have some swimming ability and also may be able to migrate vertically exposing them to different current systems, a passive particle model gives us a basis for estimating dispersal. Mitsuhiro Kawase has been working on such models in Puget Sound for several years, and will use them to find Nemo. He has already produced some preliminary data that suggest that particles released at Point Heyer, Vashon Island, do not move very far and seem to circle Vashon Island.

We will test these predictions with oceanographic drifters this year (2007). These are small buoys which have a sail (drogue) hanging beneath them so they follow currents rather than the wind. They transmit their GPS coordinates to a satellite which allows us to follow them in real time and to compare their trajectories with the model.

If you find these drifters in the water, please leave them alone. If you find them stranded on a beach, please let us know by sending an e-mail to lhauser@u.washington.edu. Ideally, please send GPS coordinates or an accurate description of the site.

Three drifters were deployed on Aug 14, 2007 during ebb (drifter 1), low slack (drifter 2) and flood tide (drifter 3). Here are some photos of the drifters.

Have a look at maps of a drifter path of our three drifters over the first 5 days of the experiment (Aug 14-19, 2007). From these data we can predict ocean currents during the larval period of rockfish.

dispersal model
Distribution of particles released from Point Heyer, Vashon Island, after two weeks from a current model of Puget Sound. The map also shows potential sampling sites to find Nemo.

Photos of Deployment

Drifter Maps

Genetics

I have to get out of here - I have to find my son!

We can predict from oceanographic models where Nemo is going, but we need to check if it is really him who arrived. One of the methods to do that is parentage testing using genetic markers. It works the same way as paternity tests in humans, and is very similar to barcoding for price tags: each individual gets one bar from its mother and one from its father. What we need to do is match the barcode of baby rockfish with that of potential parents. There are many thousands of potential parents for each Nemo in Puget Sound, so we need to combine the barcode information from many different tags in each fish. Although this is a daunting task, we have already shown that this is feasible (read scientific article).

Similar to paternity test, our genetic tests are non-lethal, which means we can take a little fin clipping from live fish and release them again. Over the years, we hope that we'll obtain samples for most of the adult population at Point Heyer.

Once we have matched juveniles and their parents, we can estimate dispersal distances from the difference between them.

17d old rockfish
17 day old brown rockfish larva. Photo: P. Chaillé, UCSB

parentage illustration
Illustration of the genetic testing procedure. Nemo has two bars, one from dad and one from mom. We have to find the potential parents that share a band with him - in this case, it would be individuals 4 and 6.

Otolith microchemistry

Think dirty thoughts. We're gonna make this tank so filthy the dentist will HAVE to clean it.

Fish have sensory organs enabling them to perceive gravity and to maintain their position in the water. These structures are called earbones, or otoliths. Because these structures grow faster in summer and slower in winter, they can be used for ageing fish, just like trees (try the interactive ageing site of the Alaska Fisheries Science Center). The chemical composition of otoliths reflects the chemical composition of the environment at the time, and we can use this to chemically mark rockfish larve. By injecting gravid females with a strontium solution, a strontium signature is created in all larvae of that female. The injections are harmless to female and larvae, and excess strontium is excreted after a few hours from the musculature. The otolith, however, stores some of the strontium, allowing the identification of Nemo. The detection of strontium in the otolith is quite tricky - Mari Kuroki at the University of Tokyo uses a lase technique to do that (see scientific article).

Otolith position
Position of otoliths in fish larvae (arrows). Photo: Larval Fish Laboratory, Colorado State University

marked otolith
Otolith marked with strontium - yellow and red colors show higher strontium concentrations (photo: Mari Kuroki)

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