Impacts of Changes in Growth of Atlantic Herring (Clupea harengus) in Newfoundland Waters
Atlantic herring is a schooling species which inhabits the coastal waters of Newfoundland. Herring can attain a maximum length of approximately 45 cm and live for up to 20 years. Growth is rapid within the first five years and herring mature and spawn for the first time between the ages of three and five years. Having attained sexual maturity, herring normally spawn once annually thereafter. Most herring spawn either in the spring or the fall.
Herring are filter feeders and feed primarily on zooplankton. Growth rates can be affected by food availability and its inter-relationship with environmental conditions such as water temperature. Although little is known regarding annual changes in plankton abundance, annual water temperature data are available for the Newfoundland region. In summary, water temperatures were above average in the mid 1980’s, then dipped below average until the mid 1990’s and have been above average since then.
Herring are fished commercially in Newfoundland waters. Management measures include: annual quotas, fishing seasons, and a minimum allowable fish size of 29 cm total length. When this minimum was set in the 1970’s, it represented the mean length at which 50% of herring matured for the first time. As a management measure, this ensured that 50% of the herring spawned at least once before being exploited by the commercial fishery.
Over the past decade, commercial fishers in some areas have encountered increased percentages of under-sized herring in their catch and contend that herring growth rates are slower and that herring are maturing at a smaller size. They have requested that fishery managers consider reducing the minimum allowable fish size.
For simplicity, the focus is on spring spawning herring.
The primary objectives of this case study are to determine if the growth and maturation rates of Atlantic herring in Newfoundland waters have changed from 1970 to 2005, and if there are spatial differences in these changes.
The secondary objective is to examine implications of any spatial-temporal changes in growth and maturation rates on fisheries management measures. Should fishery managers reduce the minimum allowable fish size? If so, should there be spatial differences in the minimum allowable fish size?
Description of the data set
Biological samples are collected from the Newfoundland commercial herring fishery on an annual basis. Individual catches (landings) are opportunistically sampled at least for every 500 t of total commercial landings, by gear type, by area of capture, and by fishing season. When a landing is identified to be sampled, fish are selected randomly from the landing (i.e. cluster). With respect to growth and maturation rates, it is reasonable to assume that the data are random cluster samples from the population. However, the probability a fish is captured by a commercial fishing gear changes with fish size and gear type, although traps and seines are thought to catch all fish they encounter. Average length and average length-at-age in the catch may be different than in the population, and this should be considered when analyzing these data.
Frequently Asked Questions
Please check this section regularly for updates. (Updated May 28, 2007.)
- Have growth rates of Atlantic herring in Newfoundland waters, as measured by mean length at age for cohorts, decreased from 1970 to 2005?
- Are there spatial differences in any changes in growth rates?
- Has the total length at which 50% of herring mature decreased from 1970 to 2005?
- Has the age at which 50% of herring mature decreased from 1970 to 2005?
- Are there spatial differences in any changes in maturation rates?
- Are growth and maturation rates related? Some functional relationships have been proposed (e.g. He and Stewart, 2001; He and Stewart, 2002; Beverton, 1993).
For this case study, a tab delimited ASCII file Newfoundland Herring Data.dat has been created, with the following fields: 1) Year, 2) GeoArea, 3) SmpNo, 4) Month, 5) Gear, 6) Maturity, 7) Length, and 8) Age.
Field descriptors are as follows:
- Year: year of sample collection - 36 years (1970 to 2005)
- GeoArea: two areas, where north coast = 1 and south coast = 2
- SmpNo: identifier for a cluster sample
- Month: where January = 1 … December = 12
- Gear: see attached gear codes
- Maturity: indicates if a fish specimen is immature = 1 or mature = 2
- Length: total length of fish specimen (mm)
- Age: age of fish specimen (years)
- The total sample size is 317421 specimens.
- Of the total sample, 285390 specimens are mature and 32031 are immature.
- Sample numbers (SmpNo) are unique within years but not across years.
- Ages range from 0 to 11 years; 11 years represents fish aged 11+.
6 = Bar Seine
8 = Trap
10 = Purse Seine
20 = Gill Net (size unspecified)
22 = Gill Net (mesh size 2”)
23 = Gill Net (mesh size 2¼”)
24 = Gill Net (mesh size 2½”)
25 = Gill Net (mesh size 2¾”)
26 = Gill Net (mesh size = 3”)
29 = Gill Net (mesh size 2 5/8”)
- DFO, 2006. Assessment of Newfoundland east and south coast herring stocks to 2006. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2006/042.
- He, J. X. and D. J. Stewart. 2002. A stage-explicit expression of the von Bertalanffy growth model for understanding age at first reproduction of Great Lakes fishes. Can. J. Fish. Aquat. Sci. 59: 250�261
- He, J. X. and D. J. Stewart. 2001. Age and size at first reproduction of fishes: predictive models based only on growth trajectories. Ecology, 82(3), 784�791.
- Beverton, R.J.H. 1992. Patterns of reproductive strategy parameters in some marine teleost fishes. J. Fish Biol. 42(Suppl. B): 137�160.
- Chapters 1 and 4, and pg. 388-390 in Quinn, T. J. and Deriso, R. B. 1999. Quantitative fish dynamics. New York: Oxford University Press.
- Welch, D. W. and R. P. Foucher. 1988. A maximum likelihood methodology for estimating length-at-maturity with application to Pacific cod (Gadus macrocephalus) population dynamics. Can. J. Fish. Aquat. Sci. 45:333�343.
- Armstrong, M. J., Gerritsen, H. D., Allen, M. McCurdy, W. J. and J. A. D. Peel. 2004. Variability in maturity and growth in a heavily exploited stock: cod (Gadus morhua L.) in the Irish Sea. ICES Journal of Marine Science, 61: 98-112.
- Berg, E. and O. T. Albert. 2003. Cod in fjords and coastal waters of North Norway: distribution and variation in length and maturity at age. ICES Journal of Marine Science, 60: 787�797.
- Morgan, M. J. and E. B. Colbourne. 1999. Variation in maturity-at-age and size in three populations of American plaice. ICES Journal of Marine Science, 56: 673�688.