DATA Series

Summary
Examine trends and effort for the Chilean sea bass using data from the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

Objectives

• Recall the basic biology of Dissostichus eleginoides, including those characteristics that make it vulnerable to overfishing.
• Formulate catch and catch per unit effort (CPUE) of Dissostichus eleginoides and analyze the trends in these values.
• Assess the Chilean sea bass population and determine if the population is being overfished.

Introduction
Chilean sea bass is a popular menu item at restaurants and catered events, but it does not necessarily come from Chile and it certainly is not a sea bass. So what exactly is this delicious white fish and should we be eating it?

Chilean sea bass (Dissostichus eleginoides) also called Patagonian toothfish is a large predatory fish found in cold, deep sub-Antarctic waters. It lives near the seabed on continental shelves and can be found as deep as 11,500 feet, though more commonly found between 1,300 and 6,500 feet. Chilean sea bass can grow to more than 6 feet long and 200 lbs, and can live to be nearly 50 years old. It feeds on squid, shrimp and small fish. It is a slow growing fish that does not reproduce until 10-12 years of age.

Chilean sea bass is fished using a bottom trawl or longline. A bottom trawl consists of a large mesh net pulled along the bottom with otter boards at the mouth of the net to help keep the mouth open. Longlines are  just what they sound like, a very long fishing lines that are set with many hooks. For a demersal or bottom-dwelling species like D. eleginoides, a longline may have up to 40,000 hooks on it. One of the hazards of this fishing method, however, is the associated death of many seabirds, especially the albatross. As the longline is baited and deployed, seabirds dive for the bait fish and get caught on the hooks. As the line sinks to the bottom, the seabirds are dragged underwater and drown. Because of this, Australia has outlawed longline fishing of Chilean sea bass, instead permitting only trawling.

Chilean sea bass became a popular seafood item at high-end U.S. restaurants in the early 1990s when the common name was switched from Patagonian toothfish (an apparently unappetizing name). Today, this versatile fish can fetch as much as $70 per pound. But the popularity of Chilean sea bass combined with the fact that it reproduces at a relatively late age has caused stocks to become severely overfished. Management efforts for the fishery have had little impact due to excessive illegal, unreported and unregulated (IUU) fishing. It is estimated that the amount of illegally caught Chilean sea bass is one and a half times as much as that caught legally. In light of these numbers, many chefs across the country participated in the “Take a Pass on Chilean Sea Bass” campaign and removed the fish from their menus. But that was more than 15 years ago. Has the tide turned?

The Chilean sea bass fishery off Antarctica has been regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) since 1982. For this data activity, we will access catch and fishing effort data for D. eleginoides to look for evidence of overfishing.

Data Activity
The data for this activity come from the CCAMLR’s Statistical Bulletin Volume 14 published in 2002. Print out the following tables and data worksheets:

• Table 2 – Catch (tonnes) by Species
• Table 8.2 – Effort (fishing hours) by Target Species and Country
• Bridge DATA Series_Chilean Sea Bass_Worksheet

In Table 2, locate Dissostichus eleginoides. Record the catch in metric tonnes for each year in Column 1 of the worksheet and plot the values on the total reported catch graph.

In Table 8.2, located Dissostichus eleginoides (abbreviation TOP = Toothfish, Patagonian). In Column 2 of the worksheet, record the total fishing effort in hours for all countries combined. This is the bold number at the bottom of each column.

Next, we will calculate the Catch Per Unit of Effort (CPUE) for each year and record in Column 3 of the workheet. CPUE is a measurement that is used in fisheries to help analyze whether or not a fish population is being exploited or overfished. When the CPUE starts to decline, that means that less fish are being caught for the same amount of work indicating that there are fewer fish. To calculate the CPUE, divide the catch (Column 1) by the total fishing effort (Column 2). Record this number in Column 3 of the worksheet.

On the second graph sheet, plot as a two-line graph the total fishing effort and the CPUE. The left-hand axis is the scale for the fishing effort and the right-hand axis is the scale for the CPUE. Compare your graphs to the Bridge Graph of Chilean Sea Bass Harvest. Look at the trends from the graphs and see if there are any indications that the Chilean sea bass population is overfished. Classic signs of this are a steady decline in the catch amount and a steady decline in the CPUE especially if at the same time there is an increase in the amount of fishing effort.

• What general trends do you see for catch and CPUE for the early and mid 1990s?
• What general trends do you see for catch and CPUE for the late 1990s? Does there seem to be a pivotal year where there is a change in the trend? (1998/99)
• From this analysis, do you think the Chilean sea bass population is in trouble? (Keep in mind these data consist only of the reported legal catch, they do not not include catch data from any illegal, unreported or unregulated fishing). What might you do to confirm this? (Continue monitoring data).
• If you feel the Chilean sea bass population is being overfished, what recommendations would you have to rectify the situation?

Coming soon!