Fisheries Stocks and Stock Identification

Question 1

Fishery Stocks

Answer 1

• Individuals of a species are not distributed homogeneously in space or time
• Many species exhibit intraspecific population (i.e., stock) structure
• Recruitment originates from these individuals (a stock is self-recruiting)
• A stock is the group over which “vital rates” are homogeneous (growth, maturity, mortality, etc.)

Question 2

Why is it so important to understand stock structure?

Answer 2

Necessary for assessments and to understand the range of fishery interactions (connectivity).

Understanding the related, connected, and hierarchy is important to manage or assess population

Question 3

homogeneously

Answer 3

of the same or a similar kind or nature

of uniform structure or composition throughout

Question 4

Concept “The Unit Stock”

Answer 4

Ideally, a unit stock is a self-contained and self-perpetuating group, with no mixture from outside, and within which the biological characteristics and the impact of fishing are uniform. Such a unit would also be a genetic unit.

Question 5

What is the ideal unit stock?

Answer 5

both an ecological unit and an evolutionary unit

Question 6

What is the spectrum of the stock assessment?

Answer 6

Unit Stock (left ) and Panmixia (Right)

Question 7

Panmixia

Answer 7

Has the spectrum goes further from unit stock, an increase in stock interdependence (connectivity) and migration (gene flow).

Question 8

What was an important concept that came out of the Secor 2014 diagrams?

Answer 8

Time component and location of the stock can sway both the population size. It important to understand movement of a species through time and space.

Question 9

Evolutionary Stocks vs ecological stocks. What are the questions?

Answer 9

Stock identification (discrimination)
Connectivity
Mixed-stock analyses (stock composition analysis)
Unique genetic variation

Question 10

What are the methods used to infer evolutionary stock structure?

Answer 10

Meristic characters

Morphometric data

Genetic analyses
-Proteins
-DNA
-Nuclear
-Mitochondrial

Question 11

What are the methods used to infer ecological stock structure?

Answer 11

Spatial analyses of fisheries data

Natural tags
-Parasites
-Otolith elemental and stable isotope analyses
-Organic pollutants

Tagging
-Conventional
-Electronic

Question 12

How do you determine what method to use to infer stock structure?

Answer 12

Based on what the questions are, it leads to the type of technique is used.

Question 13

Morphometric and Meristic Analyses

Answer 13

Differences in relative body shape or size (morphometrics)

Differences in number of vertebrae, fin rays, scale rows, etc. (meristic data)

Question 14

What is the role of genetics vs. environment (ecophenotypic variation)?

Answer 14

Fish at the north end of the range seem to have more vertebrae

Question 15

What are the three main measurements for morphometric analyses?

Answer 15

total length, fork length, standard length.

Question 16

Genetic Analyses

Answer 16

In the absence of gene flow (migration and mating), populations will diverge genetically due to random (genetic) drift or natural selection

Analysis of genetic characters can provide insights into stock structure

Note: it does not take much gene flow to maintain genetic connectivity

Question 17

Genetic Characters and Analyses

Answer 17

Proteins (allozyme analysis)

Mitochondrial DNA (maternally inherited)

Nuclear DNA (biparentally inherited)
-Specific gene region (sequencing)
-Microsatellite analysis
-Single nucleotide polymorphism (SNP) analysis
-Next generation sequencing (NGS) –1000s of SNPs

Question 18

What are some types of tags used?

Answer 18

Conventional tags
Acoustic tags
Electronic tags

Question 19

What are some characteristics of conventional tags?

Answer 19

Movement from point or release to point of recapture

Need for sample design (where tags are deployed, likelihood of having a tag recaptured, reported, etc.)

Question 20

What are the two types of acoustic tags?

Answer 20

Passive and active

Question 21

What are the three types of electronic tags?

Answer 21

Internal archival tags
Pop-up archival tags
Spot tags

Question 22

What are the three main types of natural tags?

Answer 22

• Parasites
• Otolith Analyses
• Organic Pollutants

Question 23

Parasites as Natural Tags

Answer 23

Species composition and abundance of parasites may differ between stocks due to:
-Biogeography
-Intermediate host availability
-Fish stock life history

Presence can be used to confirm that host was in specific area

Expertise in parasite taxonomy typically difficult to find

Question 24

Natural Tags – Otolith Analyses

Answer 24

Otolith is not reworked

Concentrations of trace elements and stable isotopes vary spatially (and in many cases temporally)

If one knows conditions at the time of spawning, can assign individuals to spawning grounds

Question 25

What was one example of using Otolith Analysis?

Answer 25

Weakfish Stock Structure
- Fish from 5 estuaries along Atlantic coast w/minor differences Mg, Mn, Sr, Ba, δ13C, & δ18O

Use linear discriminant function analysis of various elements to separate 1996 YOY weakfish from estuaries

Collect 2 yr old spawning weakfish in 1998 and look at core of otolith to assign to a natal estuary

Question 26

Organic Pollutants as “Natural” Tags

Answer 26

Accumulate in fatty tissues, not metabolized (bioaccumulation)

Biomagnify in the food web → top predators have high levels

Different regional concentrations (ratios) of pollutants provide information on where an animal was feeding

Ratios change as animals move
to different feeding areas
(biomass dilution)

Provide information on mixing
and timing of movements