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Data Source
Science Branch, Fisheries and Oceans Canada (DFO)
Organizer
John Wheeler

Background

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.

Objectives

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.)
 

Research Question

Primaires :

  1. Est-ce que les taux de croissance du hareng de l’Atlantique des eaux de Terre-Neuve, tels que mesurés par la longueur moyenne pour les cohortes d’âge, ont diminué de 1970 à 2005?
  2. Est-ce qu’il y a des différences spatiales dans les changements des taux de croissance?

Secondaires :

  1. Est-ce que la longueur totale à laquelle 50% des harengs deviennent matures a diminué de 1970 à 2005?
  2. Est-ce que l’âge auquel 50% des harengs deviennent matures a diminué de 1970 à 2005?
  3. Est-ce qu’il y a des différences spatiales dans un changement quelconque de ces taux de maturation?

Tertiare :

  1. Est-ce que les taux de croissance et de maturation sont reliés? Certaines relations fonctionnelles ont été proposées (e.g. He et Stewart, 2001; He et Stewart, 2002; Beverton, 1993).

 

Variables

Pour cette étude de cas, on a créé un fichier ASCII délimité par des tabs, Newfoundland Herring Data.dat , avec les champs suivants: 1) Year, 2) GeoArea, 3) SmpNo, 4) Month, 5) Gear, 6) Maturity, 7) Length, et 8) Age.


Les descriptions des champs sont comme suit : 

  1. Year: année de la cueillette de l’échantillon - 36 ans (1970 à 2005) 
  2. GeoArea: deux régions, où côte nord = 1 côte sud= 2 
  3. SmpNo: identificateur de la grappe de l’échantillon 
  4. Month: mois, où janvier = 1 … décembre = 12 
  5. Gear: voir les codes d’agrès plus bas 
  6. Maturity: indique si un spécimen est immature = 1 ou mature = 2 
  7. Length:longueur totale d’un spécimen (mm) 
  8. Age: âge du spécimen (années)

Notes spéciales 

  • La taille totale de l’échantillon est de 317421 spécimens. 
  • Dans l’échantillon total, 285390 spécimens sont matures et 32031 sont immatures. 
  • Les numéros d’échantillons (smp_no) sont uniques dans une année mais pas à travers les années. 
  • Les âges varient de 0 à 11 ans, 11 ans représentant les poisssons âgés de 11 ans et plus.

Codes des agrès : 

6 = Seine à barre 
8 = Trappe 
10 = Seine à poche 
20 = Filet maillant (grosseur non spécifiée) 
22 = Filet maillant (grosseur de maille 2”) 
23 = Filet maillant (grosseur de maille 2¼”) 
24 = Filet maillant (grosseur de maille 2½”) 
25 = Filet maillant (grosseur de maille 2¾”) 
26 = Filet maillant (grosseur de maille = 3”) 
29 = Filet maillant (grosseur de maille 2 5/8”)

 

References
  • DFO, 2006. Assessment of Newfoundland east and south coast herring stocks to 2006. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2006/042.

Methods

  • 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.

Recent applications

  • 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.