Lamna nasus (Linnaeus 1758), Porbeagle (Lamnidae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

The Porbeagle Lamna nasus is a shark species that is specialised on following large fish schools (especially herrings), which serve as its prey. It lives pelagic in the sea but follows its prey into inshore waters and even river mouths. Porbeagles probably mate in summer; they are ovoviviparous, giving birth to 1-5 juveniles. The resilience of this species is very low, with individuals maturing at over 14 years (Fricke, 1987: 40; Froese & Pauly, 2005). The species reaches 350 cm total length, a weight of  230 kg, and an individual age of 45-46  years in an unfished population (today only 24-25 years) (Natanson et al., 2002).

2. Distribution (past and present)

Rare in the Skagerrak and the northern Kattegat, with occasional old records from Öresund and the Baltic Sea. Today it is very rare in most parts of its distribution range. Historically, it used to be most common in the western parts of HELCOM area; in the southern and central Baltic Sea, its presence is determined by salinity conditions, and the species only occurs in higher saline. However, the species is temporarily able to enter low salinity waters down to 10 psu to follow its prey organisms.

3. Importance (sub-regional, Baltic-wide, global)

This species is neither considered of local nor global importance in HELCOM area, according to the definition in HELCOM (2007).

4. Status of threat/decline

The species is threatened and its populations significantly declined throughout its distribution range in HELCOM area. Under IUCN criteria, this species is classified as critically endangered (CR) in HELCOM area, and as a HELCOM high priority species (HELCOM, 2007). The species is listed as critically endangered (CR) by Sweden, as endangered (EN) by George (2003; personal communication, 2004), and as threatened migrant (TM) in Germany. It is forbidden to fish for and land in Swedish waters.

5. Threat/decline factors

This species is threatened by fisheries (caught as by-catch in pelagic and trawl fisheries on schooling fish species like herrings). It is considered rare at present, and highly sensitive to human activities, but not a keystone species.

6. Options for improvement

Fishing methods might be optimized to reduce porbeagle by-catch. As porbagles are mainly threatened outside the HELCOM area in the the adjacent OSPAR area, OSPAR officials could be contacted to consider conservation measures for the species.

7. References

Fricke R. 1987. Deutsche Meeresfische. Bestimmungsbuch.  Hamburg (DJN), 219 pp.

Froese R. & Pauly D. (eds) 2005. FishBase. Available in: www.fishbase.org, version (11/2005).

George M.R. 2003.  Die Ost- und Nordsee als Lebensraum für Haie, Rochen und Chimären. Meer und Museum, 17: 15-24. 

HELCOM 2007. HELCOM Red list of threatened and declining species of lampreys and fish of the Baltic Sea. Baltic Sea Environmental Proceedings, No. 109, 40 pp.  Available in: http://www.helcom.fi/stc/files/Publications/Proceedings/bsep109.pdf

Natanson L.J., Mello J.J. & Campana S.E. 2002.  Validated age and growth of the probeagle shark, Lamna nasus, I the western North Atlantic Ocean.  Col. Vol. Sci. Pap. ICCAT, 54 (4): 1261-1279.