Working with Mediterranean scientists for 15 years as Technical Secretary of the GFCM, I became aware that the usual assumption of ‘Constant M’ for VPA and age structure calculations was inappropriate, given that most fisheries there are aimed at ages 1-3+ fish and invertebrates, and obviously the M-at-age for such young organisms is high and often declines steeply in the first years of life to a relatively constantlevel for older fishes, making the 'constant M' assumption inaccurate . Several attempts to arrive at a model which better reflects reality are described here.
A closely related issue suggests an alternative derivation of M-at-age vectors from fractal theory, and the papers cited describe my efforts in that direction.
in inverse chronological order.
Conserving spawners and harvesting juveniles: is this a better alternative to postponing capture until sexual maturity?
J. F. Caddy. Draft document presented at the Simposio Internacional Bioeconomía Pesquera y Acuícola; 21-24 Nov. 2016.
Scaling elapsed time: an alternative approach to modelling crustacean moulting schedules?
J.F. Caddy. Fisheries Research 63 (2003) 73–84. Departamento de recursos del Mar, CINVESTAV, Merida, Mexico. T.H. Huxley School of Environment, Earth Sciences and Engineering, University of London, London, UK. Received 29 January 2002; received in revised form 29 November 2002; accepted 29 November 2002
Reconstructing reciprocal M vectors from length cohort analysis (LCA) of commercial size frequencies of hake, and fine mesh trawl surveys over the same grounds.
Caddy, J.F. and A. Abella. (1999). Fish. Res. 41, pp 169-175.
Do natural mortality and availability decline with age? An alternative yield paradigm for juv3enile fisheries, illustrated by the hake, Merluccius merluccius fishery in the Mediterranean.
Abella, A.J., J.F. Caddy and F. Serena. (1997). Aquat. Living Resour. 10; pp 257-269.
Estimation of the parameters of the Caddy reciprocal M-at-age model for the construction of natural mortality vectors.
Abella, A., J.F.Caddy, F.Serena. (1998). Excerpt from: Dynamique des populations marines. Cahiers Options Méditerranées, 35.
Death rates and time intervals: is there an alternative to the constant natural mortality axiom?
Caddy, J.F. (1991). Revs. Fish Biol. Fisheries, 1, pp109-138.
Modelling stock-recruitment processes in crustacea: some practical and theoretical perspectives.
Caddy, J. F. (1986). Vol 43 (11), pp 2330-2344.
Method of solving for natural mortality rate for stock components with different schedules of growth and mortality.
Caddy, J.F. (1984). Can. J. Fish. Aquat. Sci. 41(8), pp1226-1230.
How Artificial Reefs Could Reduce the Impacts of Bottlenecks in Reef Fish Productivity within Natural Fractal Habitats.
John F. Caddy. Chapter 4.
Also in Regional Reviews.
The Advantages Offered by Mediterranean Shelf Habitats for the Conservation of Demersal Resources Using the Refugium Concept. I vantaggi offerti dagli habitat di piattaforma continentale per la conservazione delle risorse demersali in Mediterraneo attraverso il concetto di rifugio.
J.F. Caddy, Independent researcher. Biol. Mar. Mediterr. (2014), 21 (1): 192-208.
Also in Habitat and Environmental Studies and Stock Assessment and Ecosystems Issues.
Fractal environments select for high von Bertalanffy K‘s in crevice-dwelling fishes.
John F. Caddy. Keywords: Fractal coefficient, von Bertalanffy growth, coral reefs, resident reef fish, natural mortality-at- size.
Life history segmentation. Sardine.
Fractal environments select for high von Bertalanffy k’s in crevice-dwelling fishes.
John F. Caddy. Ciencia Pesquera (2013) 21(2): 49-56.