NWA - Chapter 9.1

## Fish Working Group Report

Chairman: Steve Kerr
Rapporteur: Jake Rice

The Fish Working group used a Draft Proposal for a study on Georges Bank as a starting point. The general objective of the proposal, as presented by Ed Cohen of NMFS, was to relate changes in cod and haddock larvae to temporal variability of vertical stratification on the Southern Flank of Georges Bank. Major components of the study proposal included:

- Moored oceanographic instruments to measure the development and dynamics of vertical stratification.
- Sampling of cod and haddock larvae (and zooplankton of similar size) using MOCNESS and hydroacoustics.
- Measurement of growth and condition of larvae.
- Target position is 80 m isobath.
- Target time period should include May.
- Study should cover periods of stormy and "quiet" weather.

The Working Group concurred all components of the study were appropriate, and the survey design was sound, to the extent it was presented. A number of suggestions were made to expand the scope and scale of the study, consistent with objectives of GLOBEC and CCC. Specific augmentations include:

- Study and sampling to relate the duration and intensity of stratification to:
  1. length of the food chain
  2. flux of particulate matter from surface to bottom. Both would enhance the trophic context of the study.
- Increased modeling of the physical oceanography, focusing particularly on:
  1. dynamics of the South Slope (esp. advection).
  2. more forcing functions (esp. storm events).
- More paleoecological studies including:
  1. quantification of fish remnants (scales, otoliths, etc.)
  2. stable isotope ratios; etc.
- Possible additional site on Georges Bank, where the physics differ in known ways.
- Include horizontal and tidal mixing dynamics with the vertical stratification dynamics.
- Comparative studies on other banks where the proximity of stratified and mixed waters is different. (It was suggested Georges Bank may be atypical, with the upper layer nutrient levels augmented from adjacent mixed waters.)

The discussion of Cohen's proposal evolved into a more general discussion. From the wide-ranging comments several general suggestions emerged. These should outline general areas of priority research, and guide development of additional specific proposals in many contexts, including both GLOBEC and CCC.

It was acknowledged that to evaluate marine aspects of global change we require a much more in-depth picture of the physics of all banks, to establish a background for any other work. the physical studies should focus on several factors, including:

- Mechanisms of retention and export on the banks.
- Sites of retention and export on the banks.
- The role and frequency of episodic events (storms).
- Features of transport, including how much, where, and when within the year.

The Working Group concurred that it was important to consider the effect of global change on the total energy in the ecosystem (a concept discussed by Louis Legendre, among others, recently). Questions within this context would include:

- What are the dissipative mechanisms in the system?
- What are the concentrating mechanisms in the system?
- How will those mechanisms change in magnitude?
- How will those mechanisms change in position?

No specific studies were proposed within this total energy framework, but the framework should be considered carefully in planning any global change studies in marine systems.

The Working Group suggested researchers consider any study of marine consequences of climate change in the context of another set of questions. One should ask if global change will produce:

- The same events as in recent history, but in different places in the bank/shelf, etc.
- The same events as in recent history, but at different times within the annual cycle.
- The same types of events, but of greater or lesser magnitude.
- Different events.

The Working Group then had a long discussion of the gaps in understanding of the effects of global change on adult fish. Although discussions commonly settle quickly into studies of early life history and recruitment processes, adults may be affected in many ways, and most processes are poorly understood, poorly quantified, and poorly modeled. It was noted that work planned by OPEN will address many of these problems, but additional work is appropriate. Among the foci for future directed research are:

- Studies of stock structure, to delineate the populations to be studied. Studies on Georges Bank should be a priority. Many of the new molecular and biochemical techniques should be explored. These may provide many insights beyond basic questions of stock structure.
- Studies of the direct effects of temperature on many biological processes, such as growth rate, seasonal energy budgets, and stage duration of life history stages.
- Studies of overwintering energetics are especially needed. It is important to separate the environmental and heritable components of growth rate for stocks, given the noteworthy differences in growth rate observed for many fish stocks.
- Studies of how global change may alter food and feeding patterns. The prey spectrum may change, and should be quantified. Growth efficiency varies with type of food. This must be quantified for various stocks, and the balance of prey of different quality needs to be considered in global change models. Research should address the question of whether changes in net productivity will keep up with the changes in physiological requirements.
- Research is needed to quantify the "growth window" (the period of rapid feeding and growth in most cod stocks in summer), and how it will be extended and moved in time by global change.
- Much knowledge needs to be systematized into models. Development of a full annual energy budget of cod is needed urgently.
- Commercial fisheries have marked effects on the population dynamics of many stocks, including all cod and haddock stocks. These effects must be included in meaningful models, but many consequences of fishing pressures on fish biology are poorly known.
- Research is needed to determine exactly what features (presumably physical, but not necessarily only physical) characterize spawning sites of the species of interest. Research is then needed to determine the mechanisms used by adults to find these spawning sites; the mechanisms and/or cues used by adults to aggregate the sites; and the retention mechanisms for other stages which may be present at the sites.
- Research is also needed on the basic temperature preferences and tolerances of cod (and other fish) and the behavioral mechanisms used to select and maintain position in water masses of particular characteristics. Features which must be considered include absolute vs. relative temperature selection, and importance of temperature profile vs. simply bottom temperature (the usual variable considered in studies). Features of the water masses other than temperature should be reviewed, including but not restricted to salinity.

The Working Group acknowledged that there are many excellent data sets on fish populations; many extending for decades, some for centuries. These data sets are often collected for specific purpose, usually stock assessments, and are greatly underutilized for other purposes, including global change impacts. Major analysis projects should be initiated to make more use of these historic resources. Candidate projects include:

- The degree to which Sequential Population Analyses smooth yearclass variation. This has been shown to occur, but to unspecified degrees, for most stocks. If year-class variation is smoothed by SPA, individual population estimates will be poor data for examining linkages between population and environmental attributes.
- What is the true measure of spawning output (spawning biomass? egg production?) and how is it related to recruitment levels?
- How far can one hindcast the physics and biology from existing data sets of catches and temperature records which may be long, but of uneven or unknown quality?
- The research vessel surveys for groundfish have been conducted for decades on every bank from New York Bight to Northern Labrador and Greenland. Methods are quite comparable among most surveys, and individual surveys are usually highly consistent. These data are invaluable, and should be analyzed much more comprehensively. In particular, they should be used to investigate how the pattern of aggregation varies with time, stock size and oceanographic conditions, and much more extensive use should be made of the oceanographic data collected on most of these surveys. Rarely are more than bottom temperatures analyzed, although profiles are often collected. Even bottom temperatures are usually examined as only absolute temperature, and the regime from which the fish select sites is rarely considered. The Working Group RECOMMENDS that a Working Group be established with scientists from the entire Atlantic coast, to ensure that appropriate and comprehensive analyses of these data are conducted, and the analyses be done with proper statistical tools consistently for data from New England to Greenland.
- Many additional historical data sets of fish populations and oceanographic attributes exist. Data "archaeology" should be done to evaluate the quality of these data, and make good data sets available to the scientific community.
- Much has been learned from the small amount of work done on marine paleoecological cores. More of this work should be done.

The Working Group concurred that bottom substrate was important to many (probably all) life history stages of fish, as it is to benthos. Substrate characteristics are also poorly known for most areas. Research is urgently needed for to quantify substrate attributes on meaningful spatial scales. Then studies are needed to establish and quantify the linkages of the substrate attributes to each life history stage of fish. This quantification is important in the global change context both as a covariate (so data can be interpreted in meaningful ways), and because substrate characteristics may be altered by global change processes (altered erosion, deposition and sedimentation regimes).

The Working Group also reviewed technological needs from the fish study perspective. Many deficiencies were noted in both hardware and software tools. Among the requirements are:

Hardware:

- Fast, affordable tools for biogeochemical analyses of cores.
- Tools for rapid quantitative analyses of plankton samples and hydroacoustic signals.
- Image analyses systems for many purposes, especially for sorting, identifying and quantifying plankton samples.
- More research and development on all aspects of hydroacoustics. Determining absolute abundance, and automated species identification from hydroacoustic signals are urgent needs.

Software:

- Better use of quantitative experimental design theory and practice in research projects.
- More software for processing of the huge amounts of data collectable with hydroacoustics.
- Statistical tools are inadequate for relating the multidimensional patterns in the biology and physics data sets. Processes are nonlinear, have thresholds, plateaus, asymmetries, and many other characteristics which are handled very poorly by commonly used regression-based statistical tools.
- Uncertainty is handled very poorly by most quantitative tools in both fisheries and physical oceanography. This must be improved before any model predictions can be subjected to meaningful quantitative tests.

The Working Group concluded with a second wide-ranging overview discussion. Three other general points emerged, the first two with relevance to the entire GLOBEC/CCC community. We need much more efficient methods to mobilize the existing data in every discipline, and produce data products which will be useful to other disciplines, as well as the specialists in one field. We need much more efficient ways of getting experts from diverse disciplines to come together often, and to work together. Finally the group agreed it would be necessary, at some point, to quantify the predators on, and prey of, fish larvae, juveniles, and adults; and the population dynamics consequences of the predator-prey interactions. That is not going to be an easily tractable problem.

As the Working Group adjourned, it agreed to RECOMMEND to the GLOBEC Steering Committee that it develop many of the general observations in this report into specific recommendations for Working Groups or other fora to ensure experts come together to proceed further with the work outlined in this report.