1. Dan Minchin Marine Organism Investigations, Ireland ERASMUS Course: Coastal Research and Planning Institute, University of Klaipeda, Lithuania, October 2012

2. Growth varies throughout the year and rings can be laid down: In winter When spawning When disturbed Often not clear First ring can be difficult

3. Different types of scale Not always easy to age Spawning checks can occur Can be removed during the life of the fish

4. Otoliths are paired and the fish to be killed because the bones lie in the brain The bones are used for balance

5. The ear bone is a crystalline structure with clear rings. This bone may need to be sectioned for some fishes A microscope may needed as the bone can be small

6. Some otoliths do not need to be sectioned Many flatfish have flat easy read-bones More recently daily rings can be found. Also the chemical make-up may tell where the fish has been

7. Ceyham et al., 2007. ICES J. Mar. Sci. 64(3): 531-536

8. Other bones can be used to age fish This bone is where the jaw hinges

9. Other head bones can be used. The vertebrae can show rings along the centrum This can be a useful way to age sharks Can even be used to are and estimate growth of extinct species Geffen et al., 2010. High latitude climate variability and its effects on fishery resources as revealed by fossil cod otoliths. ICES J. Mar. Sci. 68 (6): 1081-1089

10. Some sharks have spines These can be used to age The spur dog Squalus acanthias grows faster in the Atlantic than in the Pacific ATLANTICPACIFIC

11. The European freshwater eel spends the first part of its life in the sea where the strontium to calcium ratio is high. Eels living a marine, brackish or freswater existance can be distinguished

12. Careful population stidies use the nose to the end of the hypural plate Fork-length is often used Total length mainly used in fishery biology Some fish have special measurements

13. Some species can be aged in this way but older age groups most usually merge. Best with following the youngest stages Some species such as crustacea grow abruptly following the castings of their ‘shells’

14. In some fish a very large number are born in a particular year These can be followed through in subsequent years Haddock a special example.

15. Depends on water temperature Spawning may interfere with growth and cause shock marks on shells As an organism gets larger the variability cause such effects to ‘blurr’

16. Fish have different growth preferencesThis is usually reflected in the habitat they occupy

17. Do not breed until 30-35 years Slow growing Captured when they aggregate to spawn

18. Modes are not always distinct There are some computer programmes that can separate modes from length frequency distributions

19. K is the value that is used to represent the rate of growth. Most ‘r’ strategists have a high K value

20. ‘r’ Small and short lived High fecundity Short generation time High rate of dispersal Variable population density Opportunistic Productive ‘K’ Large and long lived Low fecundity Long generation time Low rate of dispersal Stable population density Stable habitats Efficient

21. Fish in a given year are presumed to have a birthdate of 1 January Fish length gradually slows down with age, but weight may be increasing considerably The maximum theoretical length is known as L ɷ (infinity)

22. Develop age-length relationships This can be applied to a population from a known region Sexing of fish will determine sex ratios Sexes may grow at different rates (i.e. plaice)

23. Deep water surveys are difficult and time consuming May take hours to set a net on the bottom Such surveys also take commercial sized fish As a result the full range of fish from pre-recruit to marketable fish can be surveyed

24. Good fishing practice does not involve the capture of juveniles Most fishing equipment will capture fish after a certain age Young fish surveys look to capture fish at a smaller size

25. Beam trawls with a fine mesh are used to capture fish that are not marketable Used for most flatfishes or for fish living just at the bottom. i.e. red mullet Must be the same stations each year and from this an index of recruiting fish is developed

26. Often use a mid-water trawl or benthic trawl in shallow water Many have several spawning periods in a year Often occur in dense shoals

27. The total weight of fish in a stock able to reproduce Important for the sustainability of a stock Critical levels according to species are set North Sea cod

28. Different indicies according to egg development or gonad appearance Different fishes can have different indicies Can vary in their index number Maturity stage Description Females 1.Immature Ovary small, firm, no eggs visible to the naked eye 2. Maturing virgin or resting Ovary more extended, firm, small oocytes visible, giving ovary grainy appearance 3. Developing Ovary large, starting to swell the body cavity, colour varies according to species, contains oocytes of two sizes 4. Gravid large, filling or swelling the body cavity, when opened large ova spill out 5. Spent Ovary shrunken, flaccid, contains a few residual eggs and many small ova

29. The age at which 50% of the individuals become mature is termed the L50. Reproduction can vary considerably according to temperature and food availability The larger the fish the more young produced

30. Gulf II sampler Travel at 5 knots using an oblique tow The water passing through the device is measured The numbers per unit surface area is calculated

31. The amount of time spent fishing The fishing mortality (F) is the fish deaths from fishing Fishing effort and fish mortality are not linear relationships

32. Octopus grow rapidly Difficult to age Their size changes according to Fishing Mortality (F)

33. Schaefer curve The proportion of the catch declines with increased fishing effort Optimal return is – fishing at the peak of the dome.

34. Once one fishes past the peak of the dome the return is less Taking into account fuel and maintenance costs there is a tipping point where return equals outgoings

36. The yeild (catch) varies according to the effort. At the maximum return fish should have spawned The yeild increase with increased fishing effort

37. Trends in the decline of fish stocks Concerns over the future of fisheries Management measures urgently required but unpopular