Fish Marking Not in your textbook!

Reasons for marking fishes To identify stocks To assess stock size To assess growth and mortality rates Mark must have minimum interference with biology of fish while having maximum utility To identify stocks To assess stock size To assess growth and mortality rates Mark must have minimum interference with biology of fish while having maximum utility

Requirements of the mark 1) persist for life of fish 2) not interfere with behavior 3) not make fish more vulnerable to predators 4) not tangle with weeds or nets 5) easy to apply (minimize equipment, stress to fish) 6) applicable to broad range of sizes 1) persist for life of fish 2) not interfere with behavior 3) not make fish more vulnerable to predators 4) not tangle with weeds or nets 5) easy to apply (minimize equipment, stress to fish) 6) applicable to broad range of sizes

More requirements 7) variable to allow distinctive marking of groups 8) not create health hazard 9) easily detected in field by untrained people 10) inexpensive, easy to obtain 11) minimum confusion in reporting 12) remain unaffected by preservatives 13) no effect on growth or survival of fish 7) variable to allow distinctive marking of groups 8) not create health hazard 9) easily detected in field by untrained people 10) inexpensive, easy to obtain 11) minimum confusion in reporting 12) remain unaffected by preservatives 13) no effect on growth or survival of fish

Selection considerations 1) length of time 2) skill of personnel –uniform application, minimum disturbance 3) species to be tagged 4) means of recovery –commercial or sport fishery (incentive) 5) concurrent marking programs 1) length of time 2) skill of personnel –uniform application, minimum disturbance 3) species to be tagged 4) means of recovery –commercial or sport fishery (incentive) 5) concurrent marking programs

Types of marks 1) tags 2) fin clipping 3) branding 4) dye 5) tattooing 6) subcutaneous injection 7) genetic 1) tags 2) fin clipping 3) branding 4) dye 5) tattooing 6) subcutaneous injection 7) genetic

Determining the Age of Fish

Useful fish structures In temperate regions, fish growth is seasonal. Changes in growth rate are recorded in the growth of hard structures in fishes. These structures can be used to determine fish age.

Scales

Otoliths

Fin rays/spines

Cleithra

Vertebrae

Various useful structures

Back calculation Growth of fish scale is proportional to growth of fish length Length at each age can be determined from scale, if fish length is known