(b) suggest an environmental or policy change that might have caused some of these temporal shifts and cite a relevant paper as supporting evidence.

Herring larvae survival rate is intrinsically linked to their rate of drift from their birthplace around the British Isles to the more sheltered areas of the German Bright and Skagerrak, which are capable of supporting larger populations of larvae due to the spring plankton bloom \cite{B_ckmann_1950}. If the time taken to drift is too long, the larvae are vulnerable to predation or starvation. Circulation of north sea waters are driven by a number of environmental factors, including oceanic inflow from the Atlantic \cite{Turrell_1992}. Hydrographic data from this time indicates a number of anomalies in the timing of arrival of oceanic inflow coming much later compared to previous years, and has been backed up by planktonic data showing a significant reduction in transport over this time period\cite{Corten_2012}. Combined, this suggests the 1971-1979 collapse was due in part due to anomalous variance in oceanic inflow from the Atlantic.

Q2. Why might catch data like these give unreliable estimates of the true underlying population abundance and the ability to withstand increased fishing pressure?

Despite the ubiquity of recruitment as the underlying measure for estimating marine populations (due to the relative ease of counting on land compared to at sea), recruitment data is generally considered to underestimate total fish populations. Not all of a catch is landed, due to at-sea discarding of sub-optimal fish, such as juveniles. One such estimate by the FAO suggested 10% of all caught herrings, sardines & anchovies are discarded at sea; this value increases to 45% when examining flounders, halibuts & soles \cite{fao1994}. In multi-species fisheries, at-sea discards are proportionally larger due to unintentional capture of unwanted species, as well as rejection of poor quality fish of the intended species. In areas where regulations on catch size are in place, recruitment data is distorted to fit these regulations, leading to certain EEA jurisdictions to climate use of recruitment data as a measure of populations \cite{Cook_2013}.

Q3. (a) Based on current global IUCN status and other sources, which is globally the most vulnerable species in your dataset, and why?

 Haddock is currently listed as vulnerable on the IUCN red list, on the basis of previous observed population reduction and projected levels of future population reduction based on potential levels of exploitation (A1 + A2d) \cite{j1996}. The last IUCN estimate took place in 1996, and is in need of updating; however current trends indicate overfishing of haddock is continuing on a global scale, as recently as 2017, the EU and Norway agreeing to reduce haddock catches for 2017, due to a report from ICES indicating significant population declines \cite{ices2018}.

(b) from your dataset what is the minimum catch for this species, expressed as a % of its peak, across your time series?

 The minimum landings value recorded, which is from 2008 represents only 4.69% of the peak recruitment value, which was collected 39 years earlier in 1969.

(c) Name a key species trait that is commonly related to vulnerability to overfishing for one of the species in Table 1, explain briefly why this trait makes it vulnerable, and cite the source of information related to that named species (e.g. FishBase; Harvard-cited paper; ICES reports etc).

Large body size is associated with vulnerability to overfishing, in part because large body size requires more growth (and sometimes, but not necessarily, more time) before sexual maturity. This is in part because larger individuals are easier to be caught by conventional fishing methods \cite{Pinsky2011}. Saithes have a particularly large body size compared to the other species in the dataset, and this trait in saithes has been specifically linked to an increased risk of over-fishing in North-East Atlantic \cite{Jennings_1998}.

d) Can you find any published evidence of a named species trait (different from the one you have already selected above) that has been linked to declining landings in the N Sea

 Age at maturity has been theoretically vulnerability to overfishing vulnerability, using models with a fixed mortality rate \cite{Cardinale_1999}. Unfortunately, I've been unable to locate a paper that specifically links this with declining landings in the North Sea, however I have found a paper that links specifically a) an increase in overfishing vulnerability in species with a later age at maturity b) examination of population trends across a range of north sea fish stock, including the north sea saithe c) Identification of the north sea saithe as a fish that's at risk of overfishing and to experience relative declines in future years \cite{Jennings_1998}.

Q4. a) Construct a simple food web, either graphically or as a feeding matrix, for ONLY the 8 species in your database.