Assessment of Day Octopus (Octopus cyanea, Gray 1849) Fisheries Characteristics in Zanzibar
Keywords:
Octopus cyanea, growth, mortality, recruitment, ZanzibarAbstract
The day octopus (Octopus cyanea, Gray 1849), a major commercially exploited reef species in Zanzibar, has
recently been characterized by limited information on stock status, ideal to inform effective management
policies. This study examined the O. cyanea growth, mortality rates, and recruitment patterns in Matemwe
and Michamvi, Zanzibar, using Dorsal Mantle Length (DML) frequency data from catch landings between
October 2020 and September 2021. Octopus sizes ranged from 2 to 10.5 cm DML with an average body weight
of 2.2 kg ± 0.02 kg in Matemwe and 2.1 kg ± 0.01 kg in Michamvi. The Growth Coefficients (K) were 1.8 year⁻¹
and 2.3 year⁻¹, with Asymptotic Lengths (L∞) of 10.5 cm and 9.5 cm, and Growth Performance Indices (Φ') of
2.33 and 2.4 for Matemwe and Michamvi, respectively, typically reflecting fast growth rates. In Matemwe,
total mortality (Z) was 6.96 year~1, with natural mortality (M) of 4.20 year~1, fishing mortality (F) of 2.76
year
~1, and exploitation rate (E) of 0.40 year~1. In contrast, at Michamvi, Z was 5.75 year~1, M was 3.48 year~1
,
and F was 2.27 year~1, E was 0.39 year~1 all of which suggest a sustainable harvesting rate in line with current
management practices. Recruitment occurred year-round, with notable peaks in April at Matemwe and
February at Michamvi, reflecting the influence of geographical and human-related factors on recruitment.
This study emphasizes the need for improved management policies to mitigate the effects of intense fishing
pressure on O. cyanea in Zanzibar. Management options such as size restrictions, and fishery closures should
be enhanced to balance exploitation with regenerating capacity, ensuring the sustainability of the fishery
Downloads
References
S. Rocliffe and A. Harris, “The status of octopus fisheries in the Western Indian Ocean.,” 2016.
M. Guard, “Biology and fisheries status of octopus in the Western Indian Ocean and the Suitability for
marine stewardship council certification,” United Nations Environment Programme (UNEP) and The
Institute for Security Studies (ISS), no. June, p. 1-21, 2009.
M. A. Chande, Y. D. Mgaya, L. B. Benno, and S. M. Limbu, "The influence of environmental variables
on the abundance and temporal distribution of Octopus cyanea around Mafia Island, Tanzania", Fish.
Res., vol. 241, pp. 105991, 2021.
A. M. Peterson and S. M. Stead, “Rule breaking and livelihood options in marine protected
areas,” Environ. Conserv., vol. 38, no. 3, pp. 342–352, 2011.
K. Schreckenberg, G. Mace, and M. Poudyal, Ecosystem services and poverty alleviation:
Trade-offs and governance. New York: Routledge, 2018.
N. S. Jiddawi and M. C. Öhman, “Marine fisheries in Tanzania,” Ambio, vol. 31, no. 7–8, pp.
–527, 2002.
K. Lorenzen, “Population dynamics and potential of fisheries stock enhancement: Practical
theory for assessment and policy analysis,” Philos. Trans. R. Soc. B Biol. Sci., vol. 360, no.
, pp. 171–189, 2005.
S. A. Flinn and S. R. Midway, “Trends in growth modeling in fisheries science,” Fishes, vol.
, no. 1, pp. 1–18, 2021.
J. A. Hutchings and J. D. Reynolds, “Marine fish population collapses: Consequences for
recovery and extinction risk,” Bioscience, vol. 54, no. 4, pp. 297–309, 2004.
S. Khan and A. Khan, “Importance of age and growth studies in fisheries management,” Proc.
Natl. Semin. “Next Gener. Sci. Vis. 2020 Beyond,” no. October, p. 201, 2014.
K. Kwarfo-apegyah, P. K. Ofori-danson, and F. K. E. Nunoo, “Exploitation Rates and
Management Implications for the Fisheries of Bontanga Reservoir in the Northern Region of
Ghana Exploitation Rates and Management Implications for the Fisheries of Bontanga
Reservoir in the Northern Region of,” West African J. Appl. Ecol., vol. 14, no. June 2014, pp.
–24, 2008.
A. M. Peterson and S. M. Stead, “Rule breaking and livelihood options in marine protected
areas,” vol. 38, no. 3, pp. 342–352, 2011.
F. Rocha, A. Guerra, and A. F. González, “A review of reproductive strategies in
cephalopods,” Biol. Rev. Camb. Philos. Soc., vol. 76, no. 3, pp. 291–304, 2001.
É. E. Plagányi, M. D. E. Haywood, R. J. Gorton, M. C. Siple, and R. A. Deng, “Management
implications of modelling fisheries recruitment,” Fish. Res., vol. 217, no. May 2018, pp. 169–
, 2019.
W. F. V. Heukelem, “Growth and life‐span of Octopus cyanea (Mollusca: Cephalopoda),” J.
Zool., vol. 169, no. 3, pp. 299–315, 1973.
M. Guard and Y. D. Mgaya, “The artisanal fishery for Octopus cyanea Gray in Tanzania,”
Ambio, vol. 31, no. 7–8, pp. 528–536, 2002.
P. Silas, M. O, Mary A. K, Mshana, J. G., Semba M. L., Mgeleka, S. S. Kuboja, B. N.,
Ngatunga, B. P. Chande, M.A. & Matiku, “Growth, mortality, exploitation rate and recruitment
pattern of Octopus cyanea (Mollusca: Cephalopoda) in the WIO region: A case study from the
Mafia Archipelago, Tanzania.,” WIO J. Mar. Sci., vol. 20, no. 1, pp. 71–97, 2021.
D. Ahmed-babou, H. Demarcq, B. Meissa, and N. Bez, “Portfolio of distribution maps for
Octopus vulgaris off Mauritania,” Hall open science, 2023.
N. Iraba, S. Yahya, J. Mang’ena, and F. Malesa, “Comparison of growth and survival rates of
big blue octopus (Octopus cyanea, 1849) fed on natural and formulated diets in captivity,”
West. Indian Ocean J. Mar. Sci., vol. 22, no. 1, pp. 47–55, 2023.
URT, “The United Republic of Tanzania (URT), Ministry of Finance and Planning, Tanzania
National Bureau of Statistics and President’s Office - Finance and Planning, Office of the Chief
Government Statistician, Zanzibar. The 2022 Population and Housing Census: A,” 2022.
K. H. Kai, A. L. Kijazi, and S. E. Osima, “An Assessment of the Seasonal Rainfall and Its
Societal Implications in Zanzibar Islands during the Season of October to December, 2019,”
Atmos. Clim. Sci., vol. 10, no. 04, pp. 509–529, 2020.
E. R. Wulfing, S., Kadba, A., Baker-Médard, M., White, “Assessing the need for temporary
fishing closures to support sustainability for a small-scale octopus fishery,” Fish. Res., vol.
, no. May, pp. 1–17, 2024.
G. Velasco, E. G. Reis, and J. P. Vieira, “Calculating growth parameters of Genidens barbus
(Siluriformes, Ariidae) using length composition and age data,” J. Appl. Ichthyol., vol. 23, no.
, pp. 64–69, 2007.
A. I. Arkhipkin et al., “Stock assessment and management of cephalopods: Advances and
challenges for short-lived fishery resources,” ICES J. Mar. Sci., vol. 78, no. 2, pp. 714–730,
F. J. Sánchez, J. Iglesias, C. Moxica, and J. J. Otero, “Growth of Octopus (Octopus vulgaris)
males and females under culture conditions,” Aquac. water fish Cult. Shellfish Cult. water
usage, vol. 47, no. 26, pp. 244–246, 1998.
M. E. Conners and M. Levine, “Characteristics and discard mortality of octopus bycatch in
Alaska groundfish fisheries,” Fish. Res., vol. 185, no. September 2016, pp. 169–175, 2017.
D. Pauly and D. Zeller, “Sea Around Us Concepts, Design and Data,” pp. 1–45, 2015.
J. F.C. Gayanilo, P. Sparre, and D. Pauly, “Stock assessment tools II,” Fish., p. 168, 2005.
Jayson M, G. Pecl, R. Villanueva, S. National, and D. Jouffre, “Understanding octopus
growth : Patterns , variability and physioSemmenslogy,” Mar. Freshw. Res., vol. 55, no. January, pp. 367–377, 2004.
A. I. Hamad and C. A. Muhando, “Feeding habits and diet composition of Octopus cyanea
(Gray, 1849) in Zanzibar waters, Tanzania,” West. Indian Ocean J. Mar. Sci., vol. 22, no. 2,
pp. 61–73, 2023.
M. Thiaw, D. Gascuel, D. Thiao, O. T. Thiaw, and D. Jouffre, “Analysing environmental and
fishing effects on a short-lived species stock: The dynamics of the octopus Octopus vulgaris
population in Senegalese waters,” African J. Mar. Sci., vol. 33, no. 2, pp. 209–222, 2011.
A. Mannini, C. Pinto, C. Konrad, P. Vasilakopoulos, and H. Winker, “‘The Elephant in the
Room’: Exploring Natural Mortality Uncertainty in Statistical Catch at Age Models,” Front.
Mar. Sci., vol. 7, no. December, pp. 1–13, 2020.
C. Mtonga, N. Jiddawi, and D. Benjamen, “Recent rise in exploitation of Tanzanian octopuses:
a policy and management challenge,” West. Indian Ocean J. Mar. Sci., vol. 2022, no. 1, pp.
–118, 2022.
H. A. Van Nieuwenhove, A.M., Ratsimbazafy and M. Kochzius, “Cryptic diversity and limited
connectivity in octopuses: Recommendations for fisheries management,” PLoS One, vol. 14,
no. 5, pp. 1–20, 2019.
C. Jørgensen and R. E. Holt, “Natural mortality: Its ecology, how it shapes fish life histories,
and why it may be increased by fishing,” J. Sea Res., vol. 75, pp. 8–18, 2013.
D. Raberinary and S. Benbow, “The reproductive cycle of Octopus cyanea in southwest
Madagascar and implications for fisheries management,” Fish. Res., vol. 125–126, pp. 190–
, 2012.
Z. L. Jacobs et al., “Key climate change stressors of marine ecosystems along the path of the
East African coastal current,” Ocean Coast. Manag., vol. 208, no. April, 2021.
P. Jereb, C. F. E. Roper, and M. Vecchione, “FAO Species Catalogue for Fishery Purposes,”
no. January 2005, pp. 1–19, 2016.
A. F. Pearce and J. B. Hutchins, “Oceanic processes and the recruitment of tropical fish at
Rottnest Island (Western Australia),” J. R. Soc. West. Aust., vol. 92, no. 2, pp. 179–195, 2009
